JP5889996B2 - Semiconductor device - Google Patents

Description

The disclosed invention relates to a semiconductor device using a semiconductor element and a manufacturing method thereof.

Storage devices using semiconductor elements are roughly classified into a volatile type in which stored contents are lost when power is not supplied and a non-volatile type in which stored contents are retained even when power is supplied.

A typical example of a volatile storage device is a DRAM (Dynamic Random Ac).
cess memory). A DRAM stores information by selecting a transistor constituting a memory element and accumulating electric charge in a capacitor.

Based on the above-described principle, in the DRAM, when the information is read, the charge of the capacitor is lost. Therefore, every time the information is read, a write operation is required again. In addition, due to leakage current (off current) between the source and drain in the off state, charge flows out or flows into the transistor included in the memory element even when the transistor is not selected, so that data (information) The retention period is short. For this reason, another write operation (refresh operation) at a predetermined cycle
Therefore, it is difficult to sufficiently reduce power consumption. Further, since the stored contents are lost when the power supply is stopped, another storage device using a magnetic material or an optical material is required to maintain the storage for a long time.

Another example of a volatile storage device is SRAM (Static Random Access).
Memory). An SRAM uses a circuit such as a flip-flop to hold stored contents, and therefore does not require a refresh operation. In this respect, the SRAM is more advantageous than a DRAM. However, since a circuit such as a flip-flop is used, there is a problem that the unit price per storage capacity increases. Further, there is no difference from DRAM in that the stored contents are lost when power supply is lost.

A typical example of the nonvolatile memory device is a flash memory. A flash memory has a floating gate between a gate electrode of a transistor and a channel formation region, and stores data by holding electric charge in the floating gate. Therefore, a data holding period is extremely long (semi-permanent) and volatile This has the advantage that the refresh operation necessary for the volatile memory device is not required (see, for example, Patent Document 1).

However, the gate insulating layer included in the memory element is deteriorated by a tunnel current generated at the time of writing, which causes a problem that the memory element does not function after a predetermined number of writings. In order to alleviate the influence of this problem, for example, a method of making the number of writings of each storage element uniform is adopted, but in order to realize this, a complicated peripheral circuit is required. And even if such a method is adopted, the fundamental problem of lifetime is not solved. That is, the flash memory is not suitable for applications where the information rewriting frequency is high.

Further, in order to hold the charge in the floating gate or to remove the charge, a high voltage is required, and a circuit therefor is also necessary. Furthermore, there is a problem that the charge injection or removal operation takes a relatively long time and it is not easy to speed up writing and erasing.

Japanese Patent Laid-Open No. 57-105889

In view of the above problems, an object of one embodiment of the disclosed invention is to provide a semiconductor device with a new structure that can hold stored data even when power is not supplied and has no limit on the number of times of writing. One of them.

The invention disclosed in this specification and the like provides a semiconductor device including a writing transistor using an oxide semiconductor, a reading transistor using a semiconductor material different from the writing transistor, and a nonvolatile memory cell including a capacitor. To do. Writing and rewriting of information in the memory cell is performed by turning on the writing transistor to turn on one of the source electrode or the drain electrode of the writing transistor, one of the electrodes of the capacitor, and the gate electrode of the reading transistor. Is performed by supplying a potential to a node electrically connected to each other and then turning off the writing transistor to hold a predetermined amount of electric charge in the node.

One embodiment of the disclosed invention includes a first transistor, a second transistor, a capacitor,
The first transistor and the second transistor have a nonvolatile memory cell including:
The second transistor is configured to include an oxide semiconductor, includes one of a source electrode or a drain electrode of the second transistor, one of the electrodes of the capacitor, and the first transistor. A first write mode in which a first electric potential is supplied to a node that is electrically connected to the gate electrode of the first write electrode so that a predetermined amount of the first charge is held in the node; and a node that holds the first charge And a second write mode in which a predetermined amount of second charge is held in the node by supplying a second potential to the semiconductor device.

Another embodiment of the disclosed invention includes a nonvolatile memory cell including a first transistor, a second transistor, and a capacitor, and the first transistor, the second transistor, Includes a different semiconductor material, and the second transistor includes an oxide semiconductor. By turning on the second transistor, one of a source electrode and a drain electrode of the second transistor is formed. And after supplying the first potential to a node where one of the electrodes of the capacitor and the gate electrode of the first transistor are electrically connected, the second transistor is turned off, so that A first write mode in which a predetermined amount of first charge is held and a second potential is supplied to the node holding the first charge by turning on the second transistor. After, by a second transistor off,
And a second write mode in which a node holds a predetermined amount of second charge.

In the above semiconductor device, the off-state current of the second transistor is preferably lower than the off-state current of the first transistor.

In the above semiconductor device, the switching speed of the first transistor is preferably larger than the switching speed of the second transistor.

In the above semiconductor device, the second transistor has an energy gap of 3 eV.
It is preferred to comprise a larger material.

Note that in the above, a writing transistor with low off-state current is realized using an oxide semiconductor; however, the disclosed invention is not limited thereto. Materials that can achieve off-current characteristics equivalent to those of oxide semiconductors, such as wide gap materials such as silicon carbide (Eg
> 3 eV) may be applied.

Note that in this specification and the like, a nonvolatile memory cell means a state where power is not supplied.
A memory cell that can hold information for a certain period or longer (at least 1 × 10 ⁴ seconds or more, preferably 1 × 10 ⁶ seconds or more).

In the present specification and the like, the terms “upper” and “lower” do not limit that the positional relationship between the constituent elements is “directly above” or “directly below”. For example, the expression “a gate electrode over a gate insulating layer” does not exclude the case where another component is included between the gate insulating layer and the gate electrode. In addition, the terms “upper” and “lower” are merely expressions used for convenience of explanation, and include terms in which the top and bottom are interchanged unless otherwise specified.

Further, in this specification and the like, the terms “electrode” and “wiring” do not functionally limit these components. For example, an “electrode” may be used as part of a “wiring”
The reverse is also true. Furthermore, the terms “electrode” and “wiring” include a case where a plurality of “electrodes” and “wirings” are integrally formed.

In addition, the functions of “source” and “drain” may be switched when transistors having different polarities are employed or when the direction of current changes in circuit operation. Therefore, in this specification, the terms “source” and “drain” can be used interchangeably.

Note that in this specification and the like, “electrically connected” includes a case of being connected via “something having an electric action”. Here, the “thing having some electric action” is not particularly limited as long as it can exchange electric signals between connection targets.

For example, “thing having some electric action” includes electrodes, wiring, switching elements such as transistors, resistance elements, inductors, capacitors, and other elements having various functions.

Since a transistor including an oxide semiconductor has extremely small off-state current, information stored for an extremely long time can be held by using the transistor for a memory cell. That is, the refresh operation becomes unnecessary or the frequency of the refresh operation can be made extremely low, so that the power consumption of the semiconductor device including the memory cell can be sufficiently reduced. Further, stored data can be retained for a long time even when power is not supplied.

In addition, a memory cell used in a semiconductor device according to the disclosed invention does not require high voltage for writing data and there is no problem of deterioration of elements. For example, like a conventional nonvolatile memory,
Since there is no need to inject electrons into the floating gate or extract electrons from the floating gate,
There is no problem of deterioration of the gate insulating layer. That is, in the memory cell according to the disclosed invention, the number of rewritable times which is a problem in the conventional nonvolatile memory is not limited, and the reliability is greatly improved. Further, since data is written depending on the on / off state of the transistor, high-speed operation can be easily realized. In addition, there is an advantage that an operation for erasing information is unnecessary.

In addition, since a transistor including a material other than an oxide semiconductor can operate at a sufficiently high speed, operation of the semiconductor device (for example, information storage) can be performed by using the transistor in combination with a transistor including an oxide semiconductor. It is possible to sufficiently ensure the high speed of the read operation.
In addition, a transistor including a material other than an oxide semiconductor can favorably realize various circuits (such as a logic circuit and a driver circuit) that are required to operate at high speed.

As described above, a transistor including a semiconductor material other than an oxide semiconductor and a transistor including an oxide semiconductor are provided integrally, whereby a semiconductor device having unprecedented characteristics can be realized.

Circuit diagram of semiconductor device Circuit diagram of semiconductor device Circuit diagram of semiconductor device Cross-sectional view and plan view of semiconductor device Sectional drawing concerning manufacturing process of semiconductor device Sectional drawing concerning manufacturing process of semiconductor device Cross-sectional view and plan view of semiconductor device Sectional drawing concerning manufacturing process of semiconductor device Sectional drawing concerning manufacturing process of semiconductor device Cross-sectional view and plan view of semiconductor device Sectional drawing concerning manufacturing process of semiconductor device 10A and 10B illustrate electronic devices using a semiconductor device. Figure showing memory window width survey results Diagram showing characteristics of transistor using oxide semiconductor Circuit diagram for evaluating characteristics of transistors using oxide semiconductors Timing chart for evaluating characteristics of transistors using oxide semiconductors Diagram showing characteristics of transistor using oxide semiconductor Diagram showing characteristics of transistor using oxide semiconductor

An example of an embodiment of the present invention will be described below with reference to the drawings. However, the present invention is not limited to the following description, and it is easily understood by those skilled in the art that modes and details can be variously changed without departing from the spirit and scope of the present invention. Therefore, the present invention should not be construed as being limited to the description of the embodiments below.

Note that the position, size, range, and the like of each component illustrated in the drawings and the like may not represent the actual position, size, range, or the like for easy understanding. Therefore, the disclosed invention is not necessarily limited to the position, size, range, or the like disclosed in the drawings and the like.

Note that ordinal numbers such as “first”, “second”, and “third” in this specification and the like are added to avoid confusion between components and are not limited numerically. To do.

(Embodiment 1)
In this embodiment, a circuit configuration and operation of a semiconductor device according to one embodiment of the disclosed invention will be described with reference to FIGS. Note that in the circuit diagrams, an OS symbol may be added to indicate a transistor including an oxide semiconductor.

A semiconductor device illustrated in FIG. 1A-1 includes a nonvolatile memory cell including a transistor 160, a transistor 162, and a capacitor 164. In FIG. 1A-1, one of the source electrode and the drain electrode of the transistor 162, one of the electrodes of the capacitor 164, and the gate electrode of the transistor 160 are electrically connected. In addition, the first wiring (
1st Line (also referred to as a source line) and the source electrode of the transistor 160 are electrically connected, and the second wiring (2nd Line: also referred to as a bit line) and the transistor 160 are connected.
The drain electrode is electrically connected. Further, the third wiring (3rd Line:
The other of the source electrode and the drain electrode of the transistor 162 is electrically connected, and a fourth wiring (4th Line: also referred to as a second signal line) and the gate of the transistor 162 are connected. The electrode is electrically connected. The fifth wiring (5
th Line: also called a word line) and the other electrode of the capacitor 164 are electrically connected.

Here, a transistor including an oxide semiconductor is used as the transistor 162. A transistor including an oxide semiconductor has a feature that leakage current (off current) between a source and a drain in an off state is extremely small. Therefore, when the transistor 162 is turned off, one of the source electrode and the drain electrode of the transistor 162, one of the electrodes of the capacitor 164, and the gate electrode of the transistor 160 are electrically connected (hereinafter referred to as a node). , The potential of the node FG) can be held for an extremely long time.
With the capacitor 164, the charge given to the node FG can be easily held, and the held information can be easily read.

The transistor 160 is not limited by off-state current, and a transistor with a higher switching speed than the transistor 162 (for example, a larger field effect mobility value) is used to increase the operation speed of the memory cell. That is, a transistor using a semiconductor material other than an oxide semiconductor is used as the transistor 160. Note that depending on the semiconductor material selected, the off-state current of the transistor 160 may be higher than the off-state current of the transistor 162. As a semiconductor material used for the transistor 160, for example, silicon, germanium, silicon germanium, silicon carbide, gallium arsenide, or the like can be used, and a single crystal semiconductor is preferably used. The transistor 160 including such a semiconductor material can read stored information at high speed.

In the semiconductor device illustrated in FIG. 1A-1, the writing mode and the reading mode can be set by using the feature that the potential of the node FG can be held.

In the write mode in which information is stored in the memory cell, first, the potential of the fourth wiring is set to
The potential of the transistor 162 is turned on, so that the transistor 162 is turned on. Accordingly, the potential of the third wiring is supplied to the node FG, and a predetermined amount of charge is accumulated in the node FG. Here, charge that gives two different potential levels (hereinafter referred to as Low)
One of level charge and high level charge) is given.
After that, the potential of the fourth wiring is set to a potential at which the transistor 162 is turned off, so that the transistor 162 is turned off. Thus, since the node FG is in a floating state, the node F
G remains in a state where a predetermined charge is held. As described above, information can be stored in the memory cell by accumulating and holding a predetermined amount of charge in the node FG (write mode).

Since the off-state current of the transistor 162 is extremely small, the charge supplied to the node FG is held for a long time. Therefore, the refresh operation becomes unnecessary or the frequency of the refresh operation can be extremely reduced, and the power consumption can be sufficiently reduced. Further, stored data can be retained for a long time even when power is not supplied.

In a read mode in which information stored in a memory cell is read, when a predetermined potential (constant potential) is applied to the first wiring, an appropriate potential (read potential) is applied to the fifth wiring. The transistor 160 takes different states depending on the amount of charge held in the FG. In general, when the transistor 160 is an n-channel transistor, the apparent threshold V _{th_H} of the transistor 160 when the high-level charge is held at the node FG is _equal to the node FG
The apparent threshold V _t of the transistor 160 when the low level charge is held at
_This is because it becomes lower than _{h_L} . Here, the apparent threshold value means a potential of the fifth wiring which is necessary for turning on the transistor 160. Therefore, the fifth
_{Is set} to a potential V ₀ intermediate between V _{th — H} and V th — _L , whereby the node FG
Can be discriminated. For example, in the writing mode, in the case where a high-level charge is applied, the transistor 160 is turned on when the potential of the fifth wiring is V ₀ (> V _{th_H} ). If a low level charge is applied,
Even when the potential of the wiring becomes V ₀ (<V th — _L ), the transistor 160 remains in the “off state”. Therefore, the stored information can be read by reading the ON state or the OFF state of the transistor 160 (reading the potential of the second wiring) by controlling the potential of the fifth wiring (reading mode). .

Note that in the case of using memory cells arranged in an array, it is necessary to read only information of a desired memory cell. In the case where data in the memory cell is not read, a potential at which the transistor 160 is turned “off” regardless of the state of the node FG, that is, V th — _H
A smaller potential may be supplied to the fifth wiring. _{Alternatively, a} potential at which the transistor 160 is turned on regardless of the state of the node FG, that is, a potential higher than V _{th_L} may be _supplied to the fifth wiring.

Further, in the case of rewriting information stored in the memory cell, a new potential is supplied to the node FG holding a predetermined amount of charge in the above writing mode, so that the node F
G is made to hold charges related to new information. Specifically, the potential of the fourth wiring is set to a potential at which the transistor 162 is turned on, so that the transistor 162 is turned on. As a result, the potential of the third wiring (the potential related to new information) is supplied to the node FG, and the node FG
A predetermined amount of charge is stored in After that, the potential of the fourth wiring is set to a potential at which the transistor 162 is turned off and the transistor 162 is turned off, so that charge related to new information is held in the node FG. In other words, the node FG is stored in the memory cell by performing the same operation (second write mode) as the write mode in a state where a predetermined amount of charge is held in the write mode (first write mode). Information can be overwritten.

As described above, the semiconductor device according to the disclosed invention can directly rewrite information by writing information again. For this reason, it is not necessary to extract charges from the floating gate using a high voltage required in a flash memory or the like, and a reduction in operating speed due to an erasing operation can be suppressed. That is, high-speed operation of the semiconductor device is realized.

Note that the source electrode or the drain electrode of the transistor 162 is electrically connected to the gate electrode of the transistor 160, whereby the same effect as a floating gate of a floating gate transistor used as a nonvolatile memory element is obtained. When the transistor 162 is off, the node FG can be regarded as being embedded in an insulator (a so-called floating state), and electric charge is held in the node FG. Since the off-state current of the transistor 162 including an oxide semiconductor is 1 / 100,000 or less that of a transistor formed using a silicon semiconductor or the like, the loss of charge accumulated in the node FG due to leakage of the transistor 162 should be ignored. Is possible. In other words, the transistor 162 including an oxide semiconductor
A nonvolatile storage device capable of holding information even when power is not supplied can be realized.

For example, the off-state current of the transistor 162 at room temperature is 10 zA (1 zA (zeptoampere)
1 × 10 ⁻²¹ A) or less, and when the capacitance value of the capacitor 164 is about 10 fF, data can be retained for at least 10 ⁴ seconds. Needless to say, the retention time varies depending on transistor characteristics and capacitance values.

Further, in the conventional floating gate type transistor, since charge moves in the gate insulating film (tunnel insulating film) at the time of writing (rewriting), deterioration of the gate insulating film (tunnel insulating film) is inevitable. However, in the semiconductor device described in this embodiment, the transfer operation of the transistor 162 merely causes the movement of electric charge between the third wiring and the node FG, and thus degradation of the gate insulating film, which has been a problem in the past, has occurred. Can be eliminated. This means that there is no limit on the number of times of writing in principle, and the rewrite endurance is extremely high. In addition, the high voltage required for writing and erasing in the conventional floating gate type transistor is also unnecessary.

The semiconductor device illustrated in FIG. 1A-1 can be considered as illustrated in FIG. 1A-2 in which elements such as a transistor included in the semiconductor device include a resistor and a capacitor.
That is, in FIG. 1A-2, the transistor 160 and the capacitor 164 are each formed of
It is assumed that it is configured to include resistance and capacitance. R1 and C1 are a resistance value and a capacitance value of the capacitor 164, respectively, and the resistance value R1 corresponds to a resistance value by an insulating layer constituting the capacitor 164. R2 and C2 are a resistance value and a capacitance value of the transistor 160, respectively. The resistance value R2 corresponds to a resistance value by the gate insulating layer when the transistor 160 is in an ON state, and the capacitance value C2 is a so-called gate capacitance ( A gate electrode;
The capacitance formed between the source electrode and / or the drain electrode and the capacitance formed between the gate electrode and the channel formation region).

When the resistance value (also referred to as effective resistance) between the source electrode and the drain electrode when the transistor 162 is in the off state is ROS, R1 and R2 are When ROS or more and R2 satisfy ROS or more, the charge retention period (also referred to as the information retention period) is mainly determined by the off-state current of the transistor 162.

On the other hand, in the case where the above conditions are not satisfied, it is difficult to ensure a sufficient holding period even if the off-state current of the transistor 162 is sufficiently small. This is because leakage current other than off-state current of the transistor 162 (for example, leakage current generated between the source electrode and the gate electrode) is large. Thus, it can be said that the semiconductor device disclosed in this embodiment preferably satisfies the above-described relationship.

On the other hand, it is desirable that C1 and C2 satisfy the relationship of C1 or higher. This is because by increasing C1, variation in the potential of the fifth wiring can be suppressed when the potential of the node FG is controlled by the fifth wiring (for example, when reading).

By satisfying the above relationship, a more preferable semiconductor device can be realized. In addition,
R1 and R2 are controlled by the gate insulating layers of the transistor 160 and the transistor 162. The same applies to C1 and C2. Therefore, it is desirable to appropriately set the material, thickness, and the like of the gate insulating layer so that the above relationship is satisfied.

In the semiconductor device described in this embodiment, the node FG operates in the same manner as the floating gate of a floating gate type transistor such as a flash memory. However, the node FG in this embodiment is a floating gate such as a flash memory. And have essentially different characteristics. In flash memory, the voltage applied to the control gate is high.
In order to prevent the influence of the potential from reaching the floating gates of adjacent cells, it is necessary to maintain a certain distance between the cells. This is one of the factors that hinder the high integration of semiconductor devices. This factor is due to the fundamental principle of flash memory in which a tunneling current is generated by applying a high electric field.

Further, due to the above principle of the flash memory, the deterioration of the insulating film proceeds, and another problem of the limit of the number of rewrites (about 10,000 times) occurs.

A semiconductor device according to the disclosed invention operates by switching of a transistor including an oxide semiconductor and does not use the above-described principle of charge injection by a tunnel current. That is,
It is not necessary to apply a high electric field for injecting charges as in a flash memory. As a result, it is not necessary to consider the influence of the high electric field by the control gate on the adjacent cells, so the distance between the cells can be narrowed, and high integration is facilitated.

Further, since the principle of charge injection by tunneling current is not used, there is no cause for deterioration of the memory cell. That is, it has higher durability and reliability than the flash memory.

Another advantage over the flash memory is that a high electric field is unnecessary and a large peripheral circuit (such as a booster circuit) is unnecessary.

Note that in the case where the relative dielectric constant εr1 of the insulating layer included in the capacitor 164 is different from the relative dielectric constant εr2 of the insulating layer included in the transistor 160, the area S1 of the insulating layer included in the capacitor 164; In the transistor 160, the area S2 of the insulating layer constituting the gate capacitance satisfies S1 or more (preferably S2 is S1 or more), and C1 can easily realize C2 or more. In other words, it is ready to realize C1 equal to or greater than C2 while reducing the area of the insulating layer constituting the capacitor 164. Specifically, for example, in the insulating layer constituting the capacitor 164, a high dielectric constant (high-k) such as hafnium oxide.
Adopting a laminated structure of a film made of a material or a film made of a high dielectric constant (high-k) material such as hafnium oxide and a film made of an oxide semiconductor, εr1 is set to 10 or more, preferably 15 or more, and the gate capacitance In the insulating layer that constitutes, silicon oxide can be employed to satisfy εr2 = 3-4.

By using such a structure in combination, the semiconductor device according to the disclosed invention can be further highly integrated.

The above description is for the case where an n-type transistor (n-channel transistor) using electrons as a majority carrier is used. Instead of an n-type transistor, a p-type transistor (p-type transistor using holes as a majority carrier) is used. Needless to say, a channel-type transistor can be used.

As described above, a semiconductor device of one embodiment of the disclosed invention includes a writing transistor with little leakage current (off-state current) between a source and a drain in an off state, and reading using a semiconductor material different from the writing transistor And a nonvolatile memory cell including a capacitor and a capacitor.

The off-state current of the writing transistor is 100 zA (at a temperature during use (for example, 25 ° C.)).
1 × 10 ⁻¹⁹ A) or less, preferably 10 zA (1 × 10 ⁻²⁰ A) or less, and more preferably 1 zA (1 × 10 ⁻²¹ A) or less. In a normal silicon semiconductor, it is difficult to obtain a low off-state current as described above, but this can be achieved in a transistor obtained by processing an oxide semiconductor under appropriate conditions. Therefore, a transistor including an oxide semiconductor is preferably used as the writing transistor.

Further, since a transistor using an oxide semiconductor has a small subthreshold swing value (S value), the switching speed can be sufficiently increased even when the mobility is relatively low. Therefore, by using the transistor as a writing transistor, the rising edge of the writing pulse given to the node FG can be made extremely steep. In addition, since the off-state current is small, the amount of charge held in the node FG can be reduced. That is, when a transistor including an oxide semiconductor is used as a writing transistor, information can be rewritten at high speed.

Although there is no limitation on off-state current as the reading transistor, it is preferable to use a transistor that operates at high speed in order to increase the reading speed. For example, a transistor having a switching speed of 1 nanosecond or less is preferably used as the reading transistor.

Information is written into the memory cell by turning on the writing transistor so that one of the source electrode or the drain electrode of the writing transistor, the electrode of the capacitor element, and the gate electrode of the reading transistor are electrically connected. Then, a potential is supplied to the nodes connected to each other, and then the writing transistor is turned off to hold a predetermined amount of electric charge in the nodes. Here, since the off-state current of the writing transistor is extremely small, the charge supplied to the node is held for a long time. If the off-state current is substantially 0, for example, the refresh operation required in the conventional DRAM becomes unnecessary, or the frequency of the refresh operation is extremely low (for example, about once a month to once a year). Accordingly, the power consumption of the semiconductor device can be sufficiently reduced.

In addition, information can be directly rewritten by rewriting information to the memory cell. For this reason, an erasing operation required in a flash memory or the like is unnecessary, and a reduction in operating speed due to the erasing operation can be suppressed. That is, high-speed operation of the semiconductor device is realized. In addition, since a high voltage required for writing and erasing with a conventional floating gate transistor is not required, the power consumption of the semiconductor device can be further reduced. The maximum value of the voltage applied to the memory cell according to the present embodiment (the difference between the maximum potential and the minimum potential applied simultaneously to each terminal of the memory cell) is two levels (1
Bit) information is written, in one memory cell, 5V or less, preferably 3V
It is as follows.

A memory cell provided in a semiconductor device according to the disclosed invention includes a writing transistor,
It suffices to include at least a reading transistor and a capacitor, and the capacitor can be operated even when the area of the capacitor is small. Therefore, the area per memory cell is, for example,
Compared to an SRAM that requires six transistors per memory cell, the size can be made sufficiently small, and memory cells can be arranged at high density in a semiconductor device.

Further, in the conventional floating gate type transistor, since the charge moves in the gate insulating film (tunnel insulating film) at the time of writing, the gate insulating film (tunnel insulating film) is inevitably deteriorated. However, in the memory cell according to one embodiment of the present invention, information is written by holding a predetermined amount of charge in the node by the switching operation of the writing transistor. Degradation can be eliminated. This means that there is no limit on the number of times of writing in principle, and the rewrite endurance is extremely high. For example, the memory cell according to one embodiment of the present invention is 1 × 10 ⁹ times (
Even after writing (1 billion times) or more, no deterioration is observed in the current-voltage characteristics.

Furthermore, when a transistor using an oxide semiconductor is used as a writing transistor of a memory cell, the oxide semiconductor has a large energy gap of 3.0 to 3.5 eV and may have very few thermally excited carriers. Even in a high temperature environment as high as 150 ° C., the current-voltage characteristics of the memory cell are not deteriorated.

As a result of intensive studies, the present inventors have found that a transistor using an oxide semiconductor does not cause deterioration of characteristics even at a high temperature of 150 ° C., and has an excellent off current of 100 zA or less at room temperature. It was found for the first time that it has characteristics. In one embodiment of the disclosed invention, a transistor having such excellent characteristics is applied as a writing transistor of a memory cell, and a semiconductor device having characteristics that are not conventionally provided is provided.

Note that the structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

(Embodiment 2)
In this embodiment, application examples of the semiconductor device described in the above embodiment will be described with reference to FIGS.

2A and 2B illustrate the semiconductor device (hereinafter referred to as a memory cell 1) illustrated in FIG.
Also described as 90. 1 is a circuit diagram of a semiconductor device formed using a plurality of (). FIG. 2A is a circuit diagram of a so-called NAND semiconductor device in which memory cells 190 are connected in series. FIG. 2B is a so-called NOR type semiconductor device in which memory cells 190 are connected in parallel. It is a circuit diagram of a semiconductor device.

The semiconductor device illustrated in FIG. 2A includes a source line SL, a bit line BL, a first signal line S1, a plurality of second signal lines S2, a plurality of word lines WL, and a plurality of memory cells 190. FIG.
) Has a structure having one source line SL and one bit line BL. However, the present invention is not limited to this, and a structure having a plurality of source lines SL and bit lines BL may be used.

In each memory cell 190, the gate electrode of the transistor 160 and the transistor 162
One of the source electrode or the drain electrode and one electrode of the capacitor 164 are electrically connected. The first signal line S1 and the other of the source electrode and the drain electrode of the transistor 162 are electrically connected, and the second signal line S2 and the gate electrode of the transistor 162 are electrically connected. The word line WL and the other electrode of the capacitor 164 are electrically connected.

The source electrode of the transistor 160 included in the memory cell 190 is electrically connected to the drain electrode of the transistor 160 of the adjacent memory cell 190, and the drain electrode of the transistor 160 included in the memory cell 190 is connected to the drain electrode of the adjacent memory cell 190. It is electrically connected to the source electrode of the transistor 160. Note that the drain electrode of the transistor 160 included in the memory cell 190 provided at one end of the plurality of memory cells connected in series is electrically connected to the bit line. In addition, among the plurality of memory cells connected in series, the source electrode of the transistor 160 included in the memory cell 190 provided at the other end is electrically connected to the source line.

The semiconductor device illustrated in FIG. 2A performs a writing operation and a reading operation for each row. The write operation is performed as follows. The transistor 1 is connected to the second signal line S2 of the row in which writing is performed.
A potential at which 62 is turned on is applied, so that the transistor 162 in the row where writing is performed is turned on. Accordingly, the potential of the first signal line S1 is applied to the gate electrode of the transistor 160 in the designated row, and a predetermined charge is applied to the gate electrode. In this way, data can be written to the memory cell in the designated row.

The read operation is performed as follows. First, word lines WL other than the row to be read out
Further, a potential is applied to turn on the transistor 160 regardless of the charge of the gate electrode of the transistor 160, so that the transistors 160 other than the row where reading is performed are turned on.
Then, a potential (reading potential) is applied to the word line WL of the row where reading is performed so that the on state or the off state of the transistor 160 is selected by the charge of the gate electrode of the transistor 160. Then, a constant potential is applied to the source line SL, and a reading circuit (not shown) connected to the bit line BL is set in an operating state. Here, since the plurality of transistors 160 between the source line SL and the bit line BL are in an on state except for a row where reading is performed,
The conductance between the source line SL and the bit line BL is determined by the transistor 1 in the row where reading is performed.
60 states are determined. That is, the potential of the bit line BL read by the reading circuit varies depending on the charge of the gate electrode of the transistor 160 in the row where reading is performed. In this way, data can be read from the memory cell in the designated row.

The semiconductor device illustrated in FIG. 2B includes a plurality of source lines SL, bit lines BL, first signal lines S1, second signal lines S2, and word lines WL, and includes a plurality of memory cells 190. The gate electrode of each transistor 160, one of the source electrode and the drain electrode of the transistor 162, and one of the electrodes of the capacitor 164 are electrically connected. Further, the source line SL and the source electrode of the transistor 160 are electrically connected, and the bit line BL and the drain electrode of the transistor 160 are electrically connected. The first signal line S
1 and the other of the source electrode and the drain electrode of the transistor 162 are electrically connected, and the second signal line S2 and the gate electrode of the transistor 162 are electrically connected.
The word line WL and the other electrode of the capacitor 164 are electrically connected.

The semiconductor device illustrated in FIG. 2B performs a writing operation and a reading operation for each row. The writing operation is performed by a method similar to that of the semiconductor device illustrated in FIG. The read operation is performed as follows. First, the transistor 1 is connected to the word line WL other than the row to be read.
A potential at which the transistor 160 is turned off is applied regardless of the charge of the gate electrode 60, and the transistors 160 other than the row from which reading is performed are turned off. Then, a potential (reading potential) is applied to the word line WL of the row where reading is performed so that the on state or the off state of the transistor 160 is selected by the charge of the gate electrode of the transistor 160. Then, a constant potential is applied to the source line SL, and a reading circuit (not shown) connected to the bit line BL is set in an operating state. Here, the conductance between the source line SL and the bit line BL is determined by the state of the transistor 160 in the row where reading is performed. That is, the potential of the bit line BL read by the reading circuit varies depending on the charge of the gate electrode of the transistor 160 in the row where reading is performed. In this way, data can be read from the memory cell in the designated row.

Next, an example of a reading circuit that can be used for the semiconductor device illustrated in FIG.
Will be described.

FIG. 3A shows an outline of the reading circuit. The reading circuit includes a transistor and a sense amplifier circuit.

At the time of reading, the terminal A is connected to a bit line to which a memory cell to be read is connected. A bias potential Vbias is applied to the gate electrode of the transistor, and the potential of the terminal A is controlled.

The memory cell 190 has different resistance values depending on stored data. Specifically, when the transistor 160 of the selected memory cell 190 is on, the low resistance state is obtained.
When the transistor 160 of the selected memory cell 190 is in an off state, the high resistance state is obtained.

When the memory cell 190 is in a high resistance state, the potential of the terminal A becomes higher than the reference potential Vref,
The sense amplifier outputs a potential (data “1”) corresponding to the potential of the terminal A. On the other hand, when the memory cell 190 is in the low resistance state, the potential of the terminal A becomes lower than the reference potential Vref, and the sense amplifier circuit outputs a potential (data “0”) corresponding to the potential of the terminal A.

In this manner, data can be read from the memory cell 190 by using the reading circuit. Note that the reading circuit in this embodiment is an example. Other known circuits may be used. Further, the reading circuit may include a precharge circuit. A reference bit line may be connected instead of the reference potential Vref.

FIG. 3B illustrates a differential sense amplifier which is an example of a sense amplifier circuit. The differential sense amplifier has an input terminal Vin (+), an input terminal Vin (−), and an output terminal Vout.
Amplifies the difference between in (+) and Vin (−). If Vin (+)> Vin (−), Vou
t is approximately High output. If Vin (+) <Vin (−), Vout is approximately Low.
Output. When the differential sense amplifier is used for a readout circuit, Vin (+) and Vi
One of n (−) is connected to the terminal A, and the other of Vin (+) and Vin (−) is connected to the reference potential Vr.
ef is given.

FIG. 3C illustrates a latch-type sense amplifier that is an example of the sense amplifier circuit. The latch-type sense amplifier has an input / output terminal V1 and an input / output terminal V2, an input terminal for the control signal Sp, and an input terminal for the control signal Sn. First, the signal Sp is set to High and the signal Sn is set to Low to cut off the power supply potential (Vdd). Then, potentials for comparison are applied to V1 and V2. After that, when the signal Sp is set to Low, the signal Sn is set to High, and the power supply potential (Vdd) is supplied,
If the potentials V1in and V2in to be compared are in the relationship of V1in> V2in, the output of V1 is High and the output of V2 is Low, and if the relationship of V1in <V2in is satisfied, the output of V1 is Low and the output of V2 is High. It becomes. Using this relationship, V1in and V2i
The difference of n can be amplified. When the latch-type sense amplifier is used for a read circuit, one of V1 and V2 is connected to the terminal A and the output terminal via a switch, and a reference potential Vref is applied to the other of V1 and V2.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

(Embodiment 3)
In this embodiment, a structure and a manufacturing method of a semiconductor device according to one embodiment of the disclosed invention will be described with reference to FIGS.

<Cross-sectional configuration and planar configuration of semiconductor device>
FIG. 7 illustrates an example of a structure of a semiconductor device. FIG. 7A illustrates a cross section of the semiconductor device in FIG.
B) shows respective planes of the semiconductor device. Here, FIG. 7A shows A in FIG.
It corresponds to a cross section at 1-A2 and B1-B2. The semiconductor device illustrated in FIGS. 7A and 7B includes a transistor 160 using a semiconductor material other than an oxide semiconductor at a lower portion and a transistor 162 using an oxide semiconductor at an upper portion. is there. The transistor 160 using a semiconductor material other than an oxide semiconductor can operate at high speed by using a material having a field effect mobility higher than that of the oxide semiconductor material. On the other hand, the transistor 162 including an oxide semiconductor material can hold charge for a long time due to its characteristics.

Note that although all the above transistors are described as n-channel transistors, it goes without saying that p-channel transistors can be used. Further, since the technical essence of the disclosed invention is that an oxide semiconductor is used for the transistor 162 in order to retain information, the specific structure of the semiconductor device is not necessarily limited to the one shown here.

The transistor 160 in FIG. 7 includes a substrate 1 including a semiconductor material (eg, silicon).
The channel formation region 116 provided in 00, the impurity region 114 and the high-concentration impurity region 120 provided so as to sandwich the channel formation region 116 (also collectively referred to as impurity regions), and the channel formation region 116 The provided gate insulating layer 108a, the gate electrode 110a provided on the gate insulating layer 108a, the source or drain electrode 130a electrically connected to the impurity region, and the source or drain electrode 130b
Have

Here, a sidewall insulating layer 118 is provided on a side surface of the gate electrode 110a.
Further, in a region of the substrate 100 that does not overlap with the sidewall insulating layer 118 when viewed from the direction perpendicular to the surface, there is a high concentration impurity region 120 and a metal compound region 124 in contact with the high concentration impurity region 120 exists. An element isolation insulating layer 106 is provided on the substrate 100 so as to surround the transistor 160, and the interlayer insulating layer 12 is provided so as to cover the transistor 160.
6 and an interlayer insulating layer 128 are provided. Source or drain electrode 130a,
And the source or drain electrode 130b include the interlayer insulating layer 126 and the interlayer insulating layer 1
The metal compound region 124 is electrically connected through an opening formed in 28. That is, the source or drain electrode 130a and the source or drain electrode 13
0b is the high concentration impurity region 120 and the impurity region 114 through the metal compound region 124.
And are electrically connected. The electrode 130c is electrically connected to the gate electrode 110a through an opening formed in the interlayer insulating layer 126 and the interlayer insulating layer 128. Note that the sidewall insulating layer 118 may not be formed in order to integrate the transistor 160 or the like.

The transistor 162 in FIG. 7 is electrically connected to the source or drain electrode 142a, the source or drain electrode 142b, the source or drain electrode 142a, and the source or drain electrode 142b provided over the interlayer insulating layer 128. A connected oxide semiconductor layer 144; a source or drain electrode 142a; a source or drain electrode 142b; a gate insulating layer 146 covering the oxide semiconductor layer 144;
Gate electrode 1 provided over gate insulating layer 146 so as to overlap with oxide semiconductor layer 144
48a.

Here, it is preferable that the oxide semiconductor layer 144 be highly purified when impurities such as hydrogen are sufficiently removed or when sufficient oxygen is supplied. Specifically, for example, the hydrogen concentration of the oxide semiconductor layer 144 is 5 × 10 ¹⁹ atoms / c.
m ³ or less, preferably 5 × 10 ¹⁸ atoms / cm ³ or less, more preferably 5 × 10 ^1
7 atoms / cm ³ or less. Note that the hydrogen concentration in the oxide semiconductor layer 144 described above is as follows.
Secondary ion mass spectrometry (SIMS: Secondary Ion Mass Spec
roscopy). As described above, in the oxide semiconductor layer 144 in which the hydrogen concentration is sufficiently reduced to be highly purified, and the defect level in the energy gap due to the oxygen deficiency is reduced by supplying sufficient oxygen, the carrier concentration is 1 It becomes less than x10 ¹² / cm ³ , desirably less than 1 × 10 ¹¹ / cm ³ , more desirably less than 1.45 × 10 ¹⁰ / cm ³ . For example, off-state current at room temperature (here, the value per unit channel width (1 μm))
Is 100 zA / μm (1 zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less. In this manner, by using an i-type (intrinsic) or substantially i-type oxide semiconductor, the transistor 162 with extremely excellent off-state current characteristics can be obtained.

Note that in the transistor 162 in FIG. 7, the oxide semiconductor layer 144 is not processed into an island shape; thus, contamination of the oxide semiconductor layer 144 due to etching in processing can be prevented.

The capacitor 164 includes a source or drain electrode 142a, an oxide semiconductor layer 144, a gate insulating layer 146, and an electrode 148b. That is, the source or drain electrode 142 a functions as one electrode of the capacitor 164, and the electrode 148 b functions as the other electrode of the capacitor 164.

Note that in the capacitor 164 in FIG. 7, the oxide semiconductor layer 144 and the gate insulating layer 146 are stacked, whereby sufficient insulation can be ensured between the source or drain electrode 142a and the electrode 148b. .

Note that in the transistor 162 and the capacitor 164, end portions of the source or drain electrode 142a and the source or drain electrode 142b are preferably tapered. Here, the taper angle is, for example, 30 ° or more and 60 ° or less. The taper angle is a layer having a taper shape (for example, the source electrode or the drain electrode 1).
42a) shows an inclination angle formed by the side surface and the bottom surface of the layer when observed from a direction perpendicular to the cross section (a surface perpendicular to the surface of the substrate). This is because when the end portions of the source or drain electrode 142a and the source or drain electrode 142b are tapered, coverage with the oxide semiconductor layer 144 can be improved and disconnection can be prevented.

An interlayer insulating layer 150 is provided over the transistor 162 and the capacitor 164, and an interlayer insulating layer 152 is provided over the interlayer insulating layer 150.

<Method for Manufacturing Semiconductor Device>
Next, an example of a method for manufacturing the semiconductor device will be described. Hereinafter, a method for manufacturing the lower transistor 160 will be described with reference to FIGS. 8A to 8C, and then a method for manufacturing the upper transistor 162 will be described with reference to FIGS.

<Production method of lower transistor>

First, the substrate 100 including a semiconductor material is prepared (see FIG. 8A). As the substrate 100 including a semiconductor material, a single crystal semiconductor substrate such as silicon or silicon carbide, a polycrystalline semiconductor substrate, a compound semiconductor substrate such as silicon germanium, an SOI substrate, or the like can be used. Here, an example in which a single crystal silicon substrate is used as the substrate 100 including a semiconductor material is described. In general, an “SOI substrate” refers to a substrate having a structure in which a silicon semiconductor layer is provided on an insulating surface. In this specification and the like, a semiconductor layer made of a material other than silicon is provided on an insulating surface. It is used as a concept including the substrate of the configuration. That means
The semiconductor layer included in the “SOI substrate” is not limited to the silicon semiconductor layer. The SOI substrate includes a substrate in which a semiconductor layer is provided over an insulating substrate such as a glass substrate with an insulating layer interposed therebetween.

A protective layer 102 serving as a mask for forming an element isolation insulating layer is formed over the substrate 100 (see FIG. 8A). Examples of the protective layer 102 include silicon oxide and silicon nitride.
An insulating layer formed using silicon oxynitride or the like can be used. Note that an impurity element imparting n-type conductivity or an impurity element imparting p-type conductivity may be added to the substrate 100 before and after this step in order to control the threshold voltage of the transistor. . When the semiconductor is silicon, examples of the impurity imparting n-type conductivity include phosphorus (P) and arsenic (As
) Etc. can be used. Further, as an impurity imparting p-type conductivity, for example,
Boron (B), aluminum (Al), gallium (Ga), or the like can be used.

Next, etching is performed using the protective layer 102 as a mask to remove part of the substrate 100 in a region not covered with the protective layer 102 (exposed region). Thus, a semiconductor region 104 separated from other semiconductor regions is formed (see FIG. 8B). As the etching, dry etching is preferably used, but wet etching may be used.
An etching gas and an etchant can be appropriately selected according to the material to be etched.

Next, an insulating layer is formed so as to cover the semiconductor region 104, and the insulating layer in the region overlapping with the semiconductor region 104 is selectively removed, so that the element isolation insulating layer 106 is formed (see FIG. 8B). ). The insulating layer is formed using silicon oxide, silicon nitride, silicon oxynitride, or the like. As a method for removing the insulating layer, there are a polishing process such as CMP and an etching process.
Any of them may be used. Note that after the semiconductor region 104 is formed or after the element isolation insulating layer 106 is formed, the protective layer 102 is removed.

Next, an insulating layer is formed over the semiconductor region 104, and a layer containing a conductive material is formed over the insulating layer.

The insulating layer is to be a gate insulating layer later, and is obtained by using a CVD method, a sputtering method, or the like. Silicon oxide, silicon oxynitride, silicon nitride, hafnium oxide, aluminum oxide, tantalum oxide, yttrium oxide, hafnium silicate ( HfSixOy (x> 0
, Y> 0)), hafnium silicate doped with nitrogen (HfSixOy (x> 0, y>
0)), hafnium aluminate added with nitrogen (HfAlxOy (x> 0, y> 0)
) And the like. In addition, the insulating layer may be formed by oxidizing and nitriding the surface of the semiconductor region 104 by high-density plasma treatment or thermal oxidation treatment. For example, the high-density plasma treatment may include rare gases such as He, Ar, Kr, and Xe,
The reaction can be performed using a mixed gas of oxygen, nitrogen oxide, ammonia, nitrogen, hydrogen, or the like. The thickness of the insulating layer is, for example, 1 nm to 100 nm, preferably 10 nm to 50 nm.
nm or less.

The layer including a conductive material can be formed using a metal material such as aluminum, copper, titanium, tantalum, or tungsten. Alternatively, a layer including a conductive material may be formed using a semiconductor material such as polycrystalline silicon. There is no particular limitation on the formation method, and various film formation methods such as an evaporation method, a CVD method, a sputtering method, and a spin coating method can be used. Note that in this embodiment, an example of the case where the layer including a conductive material is formed using a metal material is described.

After that, the gate insulating layer 108 is selectively etched by etching the insulating layer and the layer including a conductive material.
a, a gate electrode 110a is formed (see FIG. 8C).

Next, an insulating layer 112 that covers the gate electrode 110a is formed (see FIG. 8C). And
Impurity regions 114 having a shallow junction depth are formed by adding phosphorus (P), arsenic (As), or the like to the semiconductor region 104 (see FIG. 8C). Here, phosphorus (P) or arsenic (As) is added to form an n-type transistor, but impurities such as boron (B) and aluminum (Al) are formed when a p-type transistor is formed. What is necessary is just to add an element. With the formation of the impurity region 114, a channel formation region 116 is formed below the gate insulating layer 108a of the semiconductor region 104 (see FIG. 8C). Here, the concentration of the impurity to be added can be set as appropriate. However, when the semiconductor element is highly miniaturized, it is desirable to increase the concentration. Here, the step of forming the impurity region 114 after the formation of the insulating layer 112 is employed; however, the step of forming the insulating layer 112 after the formation of the impurity region 114 may be employed.

Next, a sidewall insulating layer 118 is formed (see FIG. 8D). The sidewall insulating layer 118 is formed by forming an insulating layer so as to cover the insulating layer 112, and then the insulating layer and the insulating layer 1.
12 can be formed in a self-aligned manner by performing highly anisotropic etching treatment.
At this time, the insulating layer 112 is preferably partially etched so that the upper surface of the gate electrode 110a and the upper surface of the impurity region 114 are exposed. Note that the sidewall insulating layer 118 is formed of
It may not be formed for the purpose of high integration.

Next, an insulating layer is formed so as to cover the gate electrode 110a, the impurity regions 114, the sidewall insulating layers 118, and the like. Then, phosphorus (P), arsenic (As), or the like is added to a region in contact with the impurity region 114, so that the high-concentration impurity region 120 is formed (see FIG. 8E). After that, the insulating layer is removed, and a metal layer 122 is formed so as to cover the gate electrode 110a, the sidewall insulating layer 118, the high-concentration impurity region 120, and the like (see FIG. 8E). The metal layer 122 can be formed by various film formation methods such as a vacuum evaporation method, a sputtering method, and a spin coating method. The metal layer 122 is preferably formed using a metal material that becomes a low-resistance metal compound by reacting with a semiconductor material included in the semiconductor region 104.
Examples of such a metal material include titanium, tantalum, tungsten, nickel, cobalt, platinum, and the like.

Next, heat treatment is performed to react the metal layer 122 with the semiconductor material. Thus, a metal compound region 124 that is in contact with the high concentration impurity region 120 is formed (see FIG. 8F).
In the case where polycrystalline silicon or the like is used as the gate electrode 110a, the gate electrode 11
A metal compound region is also formed in the portion in contact with the metal layer 122 of 0a.

As the heat treatment, for example, heat treatment by flash lamp irradiation can be used. Of course, other heat treatment methods may be used, but in order to improve the controllability of the chemical reaction related to the formation of the metal compound, it is desirable to use a method capable of realizing a heat treatment for a very short time. Note that the metal compound region 124 is formed by a reaction between a metal material and a semiconductor material, and is a region in which conductivity is sufficiently increased. By forming the metal compound region, the electrical resistance can be sufficiently reduced and the device characteristics can be improved. Note that the metal layer 122 is removed after the metal compound region 124 is formed.

Next, an interlayer insulating layer 126 and an interlayer insulating layer 128 are formed so as to cover the components formed in the above steps (see FIG. 8G). The interlayer insulating layer 126 and the interlayer insulating layer 128 can be formed using a material including an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, hafnium oxide, aluminum oxide, or tantalum oxide. Alternatively, it can be formed using an organic insulating material such as polyimide or acrylic. Note that although a stacked structure of the interlayer insulating layer 126 and the interlayer insulating layer 128 is employed here, one embodiment of the disclosed invention is not limited thereto. It may be a single layer or a stacked structure of three or more layers. Interlayer insulating layer 128
After forming, it is desirable to planarize the surface by CMP, etching, or the like.

After that, an opening reaching the metal compound region 124 is formed in the interlayer insulating layer, and the source or drain electrode 130a and the source or drain electrode 130b are formed in the opening (see FIG. 8H). For example, the source or drain electrode 130a or the source or drain electrode 130b is formed by forming a conductive layer in a region including an opening using a PVD method, a CVD method, or the like, and then using the etching process or the CMP method. It can be formed by removing part of the layer.

More specifically, for example, a thin titanium film is formed by PVD in a region including the opening, and CV
A method of forming a tungsten film so as to be embedded in the opening after forming a thin titanium nitride film by the D method can be applied. Here, the titanium film formed by the PVD method reduces the oxide film (natural oxide film or the like) on the surface to be formed, and lower electrode or the like (here, the metal compound region 1).
24) has a function of reducing the contact resistance. The titanium nitride film formed thereafter has a barrier function that suppresses diffusion of the conductive material. Further, after forming a barrier film made of titanium, titanium nitride, or the like, a copper film may be formed by a plating method.

Note that when the source or drain electrode 130a or the source or drain electrode 130b is formed by removing part of the conductive layer, it is preferable that the surface be processed to be flat. For example, after thinly forming a titanium film or a titanium nitride film in a region including the opening,
In the case of forming a tungsten film so as to be embedded in the opening, unnecessary tungsten film, titanium film, titanium nitride film, and the like can be removed and the flatness of the surface can be improved by subsequent CMP. In this manner, by planarizing the surface including the source or drain electrode 130a and the source or drain electrode 130b, a favorable electrode, wiring, insulating layer, semiconductor layer, or the like can be formed in a later step. It becomes.

Note that here, the source or drain electrode 130 in contact with the metal compound region 124 is used.
Although only a and the source or drain electrode 130b are shown, in this step, an electrode in contact with the gate electrode 110a can be formed together. There is no particular limitation on a material that can be used for the source or drain electrode 130a and the source or drain electrode 130b, and various conductive materials can be used. For example, a conductive material such as molybdenum, titanium, chromium, tantalum, tungsten, aluminum, copper, neodymium, or scandium can be used. In consideration of the heat treatment performed later,
The source or drain electrode 130a and the source or drain electrode 130b are preferably formed using a material having heat resistance high enough to withstand heat treatment.

Through the above steps, the transistor 160 using the substrate 100 containing a semiconductor material is formed (see FIG. 8H). The transistor 160 using a semiconductor material other than an oxide semiconductor can operate at high speed.

Note that an electrode, a wiring, an insulating layer, or the like may be further formed after the above step. By adopting a multilayer wiring structure consisting of a laminated structure of an interlayer insulating layer and a conductive layer as a wiring structure,
A highly integrated semiconductor device can be provided.

<Method for manufacturing upper transistor>
Next, a process for manufacturing the transistor 162 over the interlayer insulating layer 128 will be described with reference to FIGS. Note that FIG. 9 illustrates manufacturing steps of various electrodes over the interlayer insulating layer 128, the transistor 162, and the like, and thus the transistor 16 existing below the transistor 162.
0 etc. are omitted.

First, a conductive layer is formed over the interlayer insulating layer 128, and the conductive layer is selectively etched, so that the source or drain electrode 142a and the source or drain electrode 142b are formed (see FIG. 9A).

The conductive layer can be formed by a PVD method such as a sputtering method or a CVD method such as a plasma CVD method. In addition, as the material of the conductive layer, aluminum, chromium, copper,
An element selected from tantalum, titanium, molybdenum, and tungsten, an alloy containing the above-described element as a component, or the like can be used. Any of manganese, magnesium, zirconium, beryllium, or a combination of these may be used. In addition, an element selected from aluminum, titanium, tantalum, tungsten, molybdenum, chromium, neodymium, and scandium, or a material obtained by combining a plurality of these elements may be used.

The conductive layer may have a single layer structure or a stacked structure of two or more layers. For example, a single-layer structure of a titanium film or a titanium nitride film, a single-layer structure of an aluminum film containing silicon, a two-layer structure in which a titanium film is laminated on an aluminum film, or a two-layer structure in which a titanium film is laminated on a titanium nitride film Examples of the structure include a three-layer structure in which a titanium film, an aluminum film, and a titanium film are stacked. Note that in the case where the conductive layer has a single-layer structure of a titanium film or a titanium nitride film, the source or drain electrode 142 a having a tapered shape and the source or drain electrode 142 are formed.
There is a merit that processing to b is easy.

The conductive layer may be formed using a conductive metal oxide. The conductive metal oxide may be abbreviated as indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), indium oxide tin oxide alloy (In ₂ O ₃ —SnO ₂ , ITO). Or indium oxide-zinc oxide alloy (In ₂ O ₃ —ZnO), or a metal oxide material containing silicon or silicon oxide.

The conductive layer is preferably etched so that end portions of the source or drain electrode 142a and the source or drain electrode 142b to be formed have a tapered shape. Here, the taper angle is preferably, for example, 30 ° or more and 60 ° or less. The gate insulating layer 14 to be formed later is formed by etching the end portions of the source or drain electrode 142a and the source or drain electrode 142b so as to have a tapered shape.
6 can be improved and step breakage can be prevented.

The channel length (L) of the transistor is determined by the distance between the source or drain electrode 142a and the lower end of the source or drain electrode 142b. Note that when performing exposure for mask formation used when a transistor having a channel length (L) of less than 25 nm is formed, extreme ultraviolet (Extreme Ultrav) having a short wavelength of several nm to several tens of nm is used.
It is desirable to use iolet). Exposure by extreme ultraviolet light has a high resolution and a large depth of focus. Therefore, the channel length (L) of a transistor to be formed later is set to 10 nm or more and 100
It is also possible to make it 0 nm (1 μm) or less, and the operation speed of the circuit can be increased. In addition, power consumption of the semiconductor device can be reduced by miniaturization.

Note that an insulating layer functioning as a base may be provided over the interlayer insulating layer 128. The insulating layer can be formed using a PVD method, a CVD method, or the like.

The source or drain electrode 142a and the source or drain electrode 1
An insulating layer may be formed on 42b. By providing the insulating layer, parasitic capacitance between a gate electrode to be formed later, the source or drain electrode 142a, and the source or drain electrode 142b can be reduced.

Next, the source or drain electrode 142a and the source or drain electrode 1
An oxide semiconductor layer 144 is formed so as to cover 42b (see FIG. 9B).

The oxide semiconductor layer 144 includes an In—Sn—Ga—Zn—O system that is a quaternary metal oxide, an In—Ga—Zn—O system that is a ternary metal oxide, and In—Sn—Zn—. O-based, In-Al-
Zn-O, Sn-Ga-Zn-O, Al-Ga-Zn-O, Sn-Al-Zn-O
In-Zn-O-based, Sn-Zn-O-based, Al-Zn-O-based, Zn-Mg-O-based, Sn-Mg-O-based, In-Mg--, which are binary metal oxides The oxide semiconductor can be formed using an O-based oxide semiconductor such as an In-O-based, Sn-O-based, or Zn-O-based oxide that is a unitary metal oxide.

Among these, an In—Ga—Zn—O-based oxide semiconductor material has sufficiently high resistance when no electric field is applied, and can sufficiently reduce off-state current. In addition, an electric field compared to a normal silicon semiconductor can be obtained. Since the effective mobility is also high, it is suitable as a semiconductor material used for a semiconductor device.

As a typical example of the In—Ga—Zn—O-based oxide semiconductor material, InGaO ₃ (ZnO)
Some are represented by _m (m> 0). Further, M is used instead of Ga, and InMO ₃ (Zn
There is an oxide semiconductor material represented as O) _m (m> 0). Here, M is gallium (Ga), aluminum (Al), iron (Fe), nickel (Ni), manganese (Mn),
One metal element or a plurality of metal elements selected from cobalt (Co) and the like are shown. For example,
M includes Ga, Ga and Al, Ga and Fe, Ga and Ni, Ga and Mn.
Ga, Co, and the like can be applied. It should be noted that the above composition is derived from the crystal structure and is merely an example.

As a target for forming the oxide semiconductor layer 144 by a sputtering method, In: Ga:
It is preferable to use one represented by a composition formula of Zn = 1: x: y (x is 0 or more and y is 0.5 or more and 5 or less). For example, In: Ga: Zn = 1: 1: 1 [atom ratio] (x = 1, y
= 1), that is, a target having a composition ratio of In ₂ O ₃ : Ga ₂ O ₃ : ZnO = 1: 1: 2 [molar ratio] can be used. In: Ga: Zn = 1: 1
: 0.5 [atom ratio] (x = 1, y = 0.5) (that is, In ₂ O ₃ : Ga ₂ O ₃
: ZnO = 1: 1: 1 [molar ratio]) or a target having a composition ratio of In: Ga: Z
n = 1: 1: 2 [atom ratio] (x = 1, y = 2), (ie, In ₂ O ₃ : Ga ₂ O
₃ : ZnO = 1: 1: 4 [molar ratio]) and a target having a composition ratio of In: Ga:
Zn = 1: 0: 1 [atom ratio] (x = 0, y = 1) (ie, In ₂ O ₃ : ZnO
A target having a composition ratio of 1: 2 [molar ratio]) can also be used.

In this embodiment, the oxide semiconductor layer 144 having an amorphous structure is formed by a sputtering method using an In—Ga—Zn—O-based metal oxide target.

The relative density of the metal oxide in the metal oxide target is 80% or more, preferably 95% or more,
More preferably, it is 99.9% or more. By using a metal oxide target having a high relative density, the oxide semiconductor layer 144 having a dense structure can be formed.

The atmosphere in which the oxide semiconductor layer 144 is formed is preferably a rare gas (typically argon) atmosphere, an oxygen atmosphere, or a mixed atmosphere of a rare gas (typically argon) and oxygen. Specifically, for example, it is preferable to use a high-purity gas atmosphere in which impurities such as hydrogen, water, hydroxyl group, and hydride are removed to a concentration of 1 ppm or less (desirably, a concentration of 10 ppb or less).

When the oxide semiconductor layer 144 is formed, for example, the object to be processed is held in a treatment chamber kept under reduced pressure, and the temperature of the object to be processed is 100 ° C. or higher and lower than 550 ° C., preferably 200 ° C. or higher and 40 ° C.
The object to be processed is heated so as to be 0 ° C. or lower. Alternatively, the temperature of the object to be processed at the time of forming the oxide semiconductor layer 144 may be room temperature. Then, a sputtering gas from which hydrogen, water, or the like is removed is introduced while moisture in the treatment chamber is removed, and the oxide semiconductor layer 144 is formed using the target. By forming the oxide semiconductor layer 144 while the object to be processed is heated, impurities contained in the oxide semiconductor layer 144 can be reduced. Further, damage due to sputtering can be reduced. In order to remove moisture in the processing chamber, an adsorption-type vacuum pump is preferably used. For example, a cryopump, an ion pump, a titanium sublimation pump, or the like can be used. Further, a turbo pump provided with a cold trap may be used. By exhausting using a cryopump or the like, hydrogen, water, or the like can be removed from the treatment chamber, so that the impurity concentration in the oxide semiconductor layer 144 can be reduced.

As a formation condition of the oxide semiconductor layer 144, for example, the distance between the object to be processed and the target is 170 mm, the pressure is 0.4 Pa, the direct current (DC) power is 0.5 kW, and the atmosphere is oxygen (oxygen 100%) Conditions such as an atmosphere, an argon (100% argon) atmosphere, or a mixed atmosphere of oxygen and argon can be used. Note that a pulsed direct current (DC) power source is preferable because dust (such as a powdery substance formed at the time of film formation) can be reduced and the film thickness can be uniform. The thickness of the oxide semiconductor layer 144 is 1 nm to 50 nm, preferably 1 nm to 30 nm, more preferably 1 nm to 10 nm. By using the oxide semiconductor layer 144 having such a thickness, a short channel effect due to miniaturization can be suppressed. However, since the appropriate thickness differs depending on the oxide semiconductor material to be applied, the use of the semiconductor device, and the like, the thickness can also be selected according to the material, the use, and the like.

Note that before the oxide semiconductor layer 144 is formed by a sputtering method, reverse sputtering in which argon gas is introduced to generate plasma is performed to form a formation surface (for example, the surface of the interlayer insulating layer 128).
It is preferable to remove the deposits. Here, reverse sputtering refers to a method of modifying the surface by causing ions to collide with the surface to be processed, instead of colliding ions with the sputtering target in normal sputtering. As a method for causing ions to collide with the processing surface, there is a method in which a high-frequency voltage is applied to the processing surface side in an argon atmosphere to generate plasma near the object to be processed. Note that nitrogen, helium,
An atmosphere of oxygen or the like may be applied.

After that, heat treatment (first heat treatment) is preferably performed on the oxide semiconductor layer 144. By this first heat treatment, excess hydrogen (including water and hydroxyl groups) in the oxide semiconductor layer 144 can be removed, the structure of the oxide semiconductor layer can be adjusted, and defect levels in the energy gap can be reduced. . The temperature of the first heat treatment is, for example, not less than 300 ° C. and less than 550 ° C., or 40
It shall be 0 degreeC or more and 500 degrees C or less.

In the heat treatment, for example, an object to be processed is introduced into an electric furnace using a resistance heating element, and under a nitrogen atmosphere,
It can be performed at 450 ° C. for 1 hour. During this time, the oxide semiconductor layer 144 is not exposed to the air so that water and hydrogen are not mixed.

The heat treatment apparatus is not limited to an electric furnace, and an apparatus for heating an object to be processed by heat conduction or heat radiation from a medium such as a heated gas may be used. For example, GRTA (Gas Rap
id Thermal Anneal) device, LRTA (Lamp Rapid The
RTA (Rapid Thermal Anneal) equipment, etc.
) Device can be used. The LRTA apparatus is an apparatus that heats an object to be processed by radiation of light (electromagnetic waves) emitted from a lamp such as a halogen lamp, a metal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high pressure mercury lamp.
The GRTA apparatus is an apparatus that performs heat treatment using a high-temperature gas. As the gas, an inert gas that does not react with an object to be processed by heat treatment, such as nitrogen or a rare gas such as argon, is used.

For example, as the first heat treatment, a GRTA process may be performed in which an object to be processed is put in a heated inert gas atmosphere and heated for several minutes, and then the object to be processed is extracted from the inert gas atmosphere. When GRTA treatment is used, high-temperature heat treatment can be performed in a short time. In addition, application is possible even under temperature conditions exceeding the heat resistance temperature of the object to be processed. Note that the inert gas may be switched to a gas containing oxygen during the treatment. This is because the defect level in the energy gap due to oxygen deficiency can be reduced by performing the first heat treatment in an atmosphere containing oxygen.

Note that as the inert gas atmosphere, an atmosphere containing nitrogen or a rare gas (such as helium, neon, or argon) as a main component and not including water, hydrogen, or the like is preferably used. For example, the purity of nitrogen or a rare gas such as helium, neon, or argon introduced into the heat treatment apparatus is 6N (99.9999%) or more, preferably 7N (99.99999%) or more (
That is, the impurity concentration is 1 ppm or less, preferably 0.1 ppm or less.

In any case, a transistor with extremely excellent characteristics can be realized by reducing impurities by the first heat treatment and forming the oxide semiconductor layer 144 that is almost i-type (intrinsic semiconductor) or i-type. it can.

By the way, the above heat treatment (first heat treatment) has an effect of removing hydrogen, water, and the like.
This heat treatment can also be referred to as dehydration treatment, dehydrogenation treatment, or the like. The dehydration treatment or the dehydrogenation treatment can be performed at a timing such as after the formation of the oxide semiconductor layer, the gate insulating layer, or the gate electrode. Further, such dehydration treatment and dehydrogenation treatment are not limited to one time, and may be performed a plurality of times.

Next, a gate insulating layer 146 in contact with the oxide semiconductor layer 144 is formed (see FIG. 9C).
. The gate insulating layer 146 can be formed by a CVD method, a sputtering method, or the like. The gate insulating layer 146 includes silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, tantalum oxide, hafnium oxide, yttrium oxide, and hafnium silicate (Hf
Si _x O _y (x> 0, y> 0)), hafnium silicate added with nitrogen (HfSi _x
O _y (x> 0, y> 0)), nitrogen-added hafnium aluminate (HfAl _x O _y
(X> 0, y> 0)) and the like are preferable. Gate insulating layer 146
May have a single layer structure or a laminated structure. Although the thickness is not particularly limited, it is preferable to reduce the thickness of the semiconductor device in order to ensure the operation of the transistor. For example, when silicon oxide is used, the thickness can be 1 nm to 100 nm, preferably 10 nm to 50 nm.

As described above, when the gate insulating layer is thin, gate leakage due to the tunnel effect or the like becomes a problem. In order to solve the problem of gate leakage, the gate insulating layer 146 is formed with hafnium oxide, tantalum oxide, yttrium oxide, hafnium silicate (HfSi _x O _y (x> 0
, Y> 0)), nitrogen-added hafnium silicate (HfSi _x O _y (x> 0, y>
0)), hafnium aluminate added with nitrogen (HfAl _x O _y (x> 0, y> 0)
), Etc., and a high dielectric constant (high-k) material may be used. By using a high dielectric constant (high-k) material for the gate insulating layer 146, the film thickness can be increased in order to suppress gate leakage while ensuring electrical characteristics. Note that a stacked structure of a film including a high dielectric constant (high-k) material and a film including any of silicon oxide, silicon nitride, silicon oxynitride, silicon nitride oxide, aluminum oxide, and the like may be employed.

After the gate insulating layer 146 is formed, second heat treatment is preferably performed in an inert gas atmosphere or an oxygen atmosphere. The temperature of the heat treatment is 200 ° C. or higher and 450 ° C. or lower, preferably 25
It is 0 degreeC or more and 350 degrees C or less. For example, heat treatment may be performed at 250 ° C. for 1 hour in a nitrogen atmosphere. By performing the second heat treatment, variation in electrical characteristics of the transistor can be reduced. In the case where the gate insulating layer 146 contains oxygen, the oxide semiconductor layer 144
Further, oxygen is supplied to the oxide semiconductor layer 144 to fill oxygen vacancies in the oxide semiconductor layer 144, whereby an i-type (intrinsic semiconductor) or an oxide semiconductor layer close to i-type can be formed.

Note that in this embodiment, the second heat treatment is performed after the gate insulating layer 146 is formed.
The timing of the second heat treatment is not particularly limited to this. For example, the second heat treatment may be performed after the gate electrode is formed. The second heat treatment may be performed after the first heat treatment, the first heat treatment may be combined with the second heat treatment, or the second heat treatment may be combined with the first heat treatment. Also good.

Next, the gate electrode 148a is formed over the gate insulating layer 146 in a region overlapping with the oxide semiconductor layer 144, and the electrode 148 is formed in a region overlapping with the source or drain electrode 142a.
b is formed (see FIG. 9D). The gate electrode 148a and the electrode 148b can be formed by forming a conductive layer over the gate insulating layer 146 and then selectively etching the conductive layer. The conductive layers to be the gate electrode 148a and the electrode 148b can be formed by a PVD method such as a sputtering method or a CVD method such as a plasma CVD method. The details are the same as in the case of the source or drain electrode 142a, etc.
These descriptions can be taken into consideration.

Next, the interlayer insulating layer 150 and the interlayer insulating layer 152 are formed over the gate insulating layer 146, the gate electrode 148a, and the electrode 148b (see FIG. 9E). The interlayer insulating layer 150 and the interlayer insulating layer 152 can be formed by a PVD method, a CVD method, or the like. Alternatively, a material including an inorganic insulating material such as silicon oxide, silicon oxynitride, silicon nitride, hafnium oxide, aluminum oxide, or tantalum oxide can be used. Note that although a stacked structure of the interlayer insulating layer 150 and the interlayer insulating layer 152 is employed in this embodiment, one embodiment of the disclosed invention is not limited thereto. It may be a single layer or a stacked structure of three or more layers.
Further, a structure in which an interlayer insulating layer is not provided is also possible.

Note that the interlayer insulating layer 152 is desirably formed so as to have a flat surface.
This is because by forming the interlayer insulating layer 152 so that the surface is flat, an electrode, a wiring, or the like can be preferably formed over the interlayer insulating layer 152 even when the semiconductor device is miniaturized. . Note that the interlayer insulating layer 152 can be planarized by a method such as CMP (chemical mechanical polishing).

Through the above steps, the transistor 162 including the highly purified oxide semiconductor layer 144 is completed (see FIG. 9E). In addition, the capacitor 164 is completed.

A transistor 162 illustrated in FIG. 9E includes an oxide semiconductor layer 144 and an oxide semiconductor layer 14.
4, a source or drain electrode 142 a, a source or drain electrode 142 b electrically connected to the gate electrode 4, a gate insulating layer 146 covering the oxide semiconductor layer 144, the source or drain electrode 142 a, the source or drain electrode 142 b, and a gate Insulating layer 146
An upper gate electrode 148a. The capacitor 164 includes a source or drain electrode 142a, an oxide semiconductor layer 144, and a source or drain electrode 142a.
And the gate insulating layer 146 covering the oxide semiconductor layer 144 and the electrode 1 over the gate insulating layer 146
48b.

In the transistor 162 described in this embodiment, since the oxide semiconductor layer 144 is highly purified, its hydrogen concentration is 5 × 10 ¹⁹ atoms / cm ³ or less, preferably 5 ×
10 ¹⁸ atoms / cm ³ or less, more desirably 5 × 10 ¹⁷ atoms / cm ³ or less. In addition, the carrier density of the oxide semiconductor layer 144 is sufficiently smaller than the carrier density (about 1 × 10 ¹⁴ / cm ³ ) in a general silicon wafer (for example, 1
× 10 ¹² / cm ³ , more preferably less than 1.45 × 10 ¹⁰ / cm ³ ).
As a result, the off-state current becomes sufficiently small. For example, the off-state current of the transistor 162 at room temperature (here, a value per unit channel width (1 μm)) is 100 zA / μm.
(1zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less.

By using the oxide semiconductor layer 144 that is highly purified and intrinsic as described above, the off-state current of the transistor can be sufficiently reduced. By using such a transistor, a semiconductor device that can hold stored data for an extremely long time can be obtained.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

(Embodiment 4)
In this embodiment, a structure and a manufacturing method of a semiconductor device according to one embodiment of the disclosed invention which are different from those in Embodiment 3 will be described with reference to FIGS.

<Cross-sectional configuration and planar configuration of semiconductor device>
FIG. 10 illustrates an example of a structure of a semiconductor device. 10A illustrates a cross section of the semiconductor device, and FIG. 10B illustrates a plan view of the semiconductor device. Here, FIG. 10 (A) is the same as FIG.
This corresponds to a cross section taken along lines A1-A2 and B1-B2 in FIG. FIG. 10A and FIG.
A semiconductor device shown in 0 (B) includes a transistor 160 using a semiconductor material other than an oxide semiconductor in a lower portion and a transistor 162 using an oxide semiconductor in an upper portion. The transistor 160 using a semiconductor material other than an oxide semiconductor can operate at high speed by using a material having a field effect mobility higher than that of the oxide semiconductor material. On the other hand, the transistor 162 including an oxide semiconductor material can hold charge for a long time due to its characteristics.

Note that although all the above transistors are described as n-channel transistors, it goes without saying that p-channel transistors can be used. Further, since the technical essence of the disclosed invention is that an oxide semiconductor is used for the transistor 162 in order to retain information, the specific structure of the semiconductor device is not necessarily limited to the one shown here.

A transistor 160 in FIG. 10 includes a channel formation region 116 provided in a substrate 100 containing a semiconductor material (eg, silicon), an impurity region 114 provided so as to sandwich the channel formation region 116, and a high-concentration impurity region 120 ( These are also simply referred to as impurity regions), a gate insulating layer 108a provided over the channel formation region 116, a gate electrode 110a provided over the gate insulating layer 108a, and a source electrically connected to the impurity region Electrode or drain electrode 130a, and source or drain electrode 130
b. Further, a wiring 142c and a wiring 142d are provided over the source or drain electrode 130a and the source or drain electrode 130b.

Here, a sidewall insulating layer 118 is provided on a side surface of the gate electrode 110a.
Further, in a region of the substrate 100 that does not overlap with the sidewall insulating layer 118 when viewed from the direction perpendicular to the surface, there is a high concentration impurity region 120 and a metal compound region 124 in contact with the high concentration impurity region 120 exists. An element isolation insulating layer 106 is provided over the substrate 100 so as to surround the transistor 160. An interlayer insulating layer 126 and an interlayer insulating layer 128 are provided so as to have an opening over the gate electrode 110 a and cover the transistor 160.
Source or drain electrode 130a, and source or drain electrode 130b
Is electrically connected to the metal compound region 124 through an opening formed in the interlayer insulating layer 126 and the interlayer insulating layer 128. That is, the source or drain electrode 130a,
The source or drain electrode 130 b is electrically connected to the high concentration impurity region 120 and the impurity region 114 through the metal compound region 124. Note that the sidewall insulating layer 118 may not be formed in order to integrate the transistor 160 or the like.

10 is electrically connected to the source or drain electrode 142a, the source or drain electrode 142b, the source or drain electrode 142a, and the source or drain electrode 142b provided over the interlayer insulating layer 128. The island-shaped oxide semiconductor layer 144 and the source or drain electrode 142 are connected to each other.
a, a source or drain electrode 142b, a gate insulating layer 146 covering the island-shaped oxide semiconductor layer 144, and a gate electrode 148a provided on the gate insulating layer 146 so as to overlap with the island-shaped oxide semiconductor layer 144 And having.

Here, the lower transistor 160 and the upper transistor 162 include a gate electrode 110a.
The source electrode or drain electrode 142a is directly formed on the upper electrode, thereby being electrically connected. That is, in the semiconductor device described in this embodiment, the upper portion of the gate electrode 110a is removed from the semiconductor device described in Embodiment 3, and the lower transistor 160 is formed.
The upper transistor 162 is formed.

Note that the oxide semiconductor layer 144 is preferably highly purified by sufficiently removing impurities such as hydrogen or by being supplied with sufficient oxygen.
Specifically, for example, the hydrogen concentration of the oxide semiconductor layer 144 is 5 × 10 ¹⁹ atoms / cm.
³ or less, preferably 5 × 10 ¹⁸ atoms / cm ³ or less, more preferably 5 × 10 ¹⁷
atoms / cm ³ or less. Note that the hydrogen concentration in the above-described oxide semiconductor layer 144 is determined by secondary ion mass spectrometry (SIMS).
oscopy). As described above, in the oxide semiconductor layer 144 in which the hydrogen concentration is sufficiently reduced to be highly purified, and the defect level in the energy gap due to the oxygen deficiency is reduced by supplying sufficient oxygen, the carrier concentration is 1 It becomes less than x10 ¹² / cm ³ , desirably less than 1 × 10 ¹¹ / cm ³ , more desirably less than 1.45 × 10 ¹⁰ / cm ³ . For example, the off current at room temperature (here, the value per unit channel width (1 μm)) is 100 zA / μm (1 zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less. Become. In this manner, by using an i-type (intrinsic) or substantially i-type oxide semiconductor, the transistor 162 with extremely excellent off-state current characteristics can be obtained.

The capacitor 164 includes a source or drain electrode 142a, an oxide semiconductor layer 144, a gate insulating layer 146, and an electrode 148b. That is, the source or drain electrode 142 a functions as one electrode of the capacitor 164, and the electrode 148 b functions as the other electrode of the capacitor 164.

Note that in the capacitor 164 in FIG. 10, the insulating property between the source or drain electrode 142a and the electrode 148b can be sufficiently ensured by stacking the oxide semiconductor layer 144 and the gate insulating layer 146. .

Note that in the transistor 162 and the capacitor 164, end portions of the source or drain electrode 142a and the source or drain electrode 142b are preferably tapered. Here, the taper angle is, for example, 30 ° or more and 60 ° or less. The taper angle is a layer having a taper shape (for example, the source electrode or the drain electrode 1).
42a) shows an inclination angle formed by the side surface and the bottom surface of the layer when observed from a direction perpendicular to the cross section (a surface perpendicular to the surface of the substrate). This is because when the end portions of the source or drain electrode 142a and the source or drain electrode 142b are tapered, coverage with the oxide semiconductor layer 144 can be improved and disconnection can be prevented.

An interlayer insulating layer 150 is provided over the transistor 162 and the capacitor 164, and an interlayer insulating layer 152 is provided over the interlayer insulating layer 150.

<Method for Manufacturing Semiconductor Device>
Next, an example of a method for manufacturing the semiconductor device will be described. Hereinafter, a process after the formation of the lower transistor 160 and a method for manufacturing the upper transistor 162 will be described with reference to FIGS. The lower transistor 160 can be manufactured by a method similar to the method described in Embodiment 3, and the description in Embodiment 3 can be referred to.

First, after the lower transistor 160 is formed by the method described in Embodiment 3, the upper portion is removed from the upper surface of the gate electrode 110a of the transistor 160 (see FIG. 11A). The portion of the transistor 160 is removed by polishing (CMP) the lower transistor 160 until the upper surface of the gate electrode 110a is exposed. Thereby, the interlayer insulating layers 126 and 128 and the source or drain electrodes 130a and 130b above the gate electrode 110a are removed. At this time, by planarizing the surface including the interlayer insulating layers 126 and 128 and the source or drain electrodes 130a and 130b, a favorable electrode, wiring, insulating layer, semiconductor layer, or the like can be formed in a later step. It becomes possible. Further, the electrode 130c described in Embodiment 3 is not necessarily formed because it is completely removed by this CMP treatment.

In this manner, the CMP process is performed to expose the upper surface of the gate electrode 110a, whereby the gate electrode 110a and the source or drain electrode 142a can be directly connected. Thus, the electrical connection between the transistor 160 and the transistor 162 is established. Can be taken easily.

Next, a conductive layer is formed over the interlayer insulating layers 126 and 128, and the conductive layer is selectively etched to form a source or drain electrode 142a and a source or drain electrode 142b.
Then, a wiring 142c and a wiring 142d are formed (see FIG. 11B). Here, the source or drain electrode 142a is the gate electrode 110a, the wiring 142c is the source or drain electrode 130a, and the wiring 142d is the source or drain electrode 130b.
And so as to be directly connected.

Here, the source or drain electrode 142a, the source or drain electrode 142
As the conductive layer for forming b, the wiring 142c, and the wiring 142d, a material similar to that described in Embodiment 3 can be used, and the description in Embodiment 3 can be referred to. Further, the etching of the conductive layer can be performed in a manner similar to the method described in Embodiment 3, and the description in Embodiment 3 can be referred to.

In addition, as described in Embodiment 3, an insulating layer may be formed over the source or drain electrode 142a and the source or drain electrode 142b. By providing the insulating layer, a gate electrode formed later and a source or drain electrode 142 are formed.
a and the parasitic capacitance between the source electrode or the drain electrode 142b can be reduced.

Next, the source or drain electrode 142a, the source or drain electrode 142b
An oxide semiconductor layer is formed so as to cover the wiring 142c and the wiring 142d, and the oxide semiconductor layer is selectively etched so as to be in contact with the source or drain electrode 142a and the source or drain electrode 142b. An oxide semiconductor layer 144 is formed (FIG. 11).
(See (C)).

The oxide semiconductor layer can be formed using a material similar to that described in Embodiment 3 by a similar method. Therefore, Embodiment 3 can be referred to for the material of the oxide semiconductor layer and the deposition method.

The oxide semiconductor layer thus formed can be etched by a method such as etching using a mask.
The island-shaped oxide semiconductor layer 144 is formed by processing into an island shape.

For etching the oxide semiconductor layer, either dry etching or wet etching may be used. Of course, both can be used in combination. The etching conditions (such as an etching gas, an etchant, etching time, and temperature) are set as appropriate depending on the material so that the oxide semiconductor layer can be etched into a desired shape.

In addition, as described in Embodiment 3, the oxide semiconductor layer 144 is subjected to heat treatment (first heat treatment).
It is desirable to do. The first heat treatment can be performed by the method described in Embodiment 3,
Embodiment 3 can be referred to. By reducing the impurities by the first heat treatment and forming the oxide semiconductor layer 144 that is almost i-type (intrinsic semiconductor) or i-type, a transistor with extremely excellent characteristics can be realized. Note that the first heat treatment may be performed before the oxide semiconductor layer is etched or after the oxide semiconductor layer is processed into an island shape by etching.

Next, the gate insulating layer 146 in contact with the oxide semiconductor layer 144 is formed (see FIG. 11C).

The gate insulating layer 146 can be formed using a material similar to that described in Embodiment 3 by a similar method. Therefore, Embodiment 3 can be referred to for a material of the gate insulating layer 146 and a deposition method.

Further, after the gate insulating layer 146 is formed, second heat treatment is preferably performed in an inert gas atmosphere or an oxygen atmosphere as described in Embodiment 3. The second heat treatment can be performed by the method described in Embodiment 3, and Embodiment 3 can be referred to. By performing the second heat treatment, variation in electrical characteristics of the transistor can be reduced. In the case where the gate insulating layer 146 contains oxygen, oxygen is supplied to the oxide semiconductor layer 144 so that oxygen vacancies in the oxide semiconductor layer 144 are filled, so that it is almost as close to i-type (intrinsic semiconductor) or i-type. An oxide semiconductor layer can also be formed.

Note that in this embodiment, the second heat treatment is performed after the gate insulating layer 146 is formed.
The timing of the second heat treatment is not particularly limited to this. For example, the second heat treatment may be performed after the gate electrode is formed. The second heat treatment may be performed after the first heat treatment, the first heat treatment may be combined with the second heat treatment, or the second heat treatment may be combined with the first heat treatment. Also good.

Next, the gate electrode 148a is formed over the gate insulating layer 146 in a region overlapping with the oxide semiconductor layer 144, and the electrode 148 is formed in a region overlapping with the source or drain electrode 142a.
b is formed (see FIG. 11D). The gate electrode 148a and the electrode 148b can be formed by forming a conductive layer over the gate insulating layer 146 and then selectively etching the conductive layer. The conductive layers to be the gate electrode 148a and the electrode 148b can be formed by a PVD method such as a sputtering method or a CVD method such as a plasma CVD method. The details are the same as those of the source electrode or the drain electrode 142a, and the description thereof can be referred to.

Next, as described in Embodiment 3, the interlayer insulating layer 150 and the interlayer insulating layer 152 are formed over the gate insulating layer 146, the gate electrode 148a, and the electrode 148b. Interlayer insulation layer 1
50 and the interlayer insulating layer 152 can be formed using a material similar to that described in Embodiment 3 by a similar method. Therefore, Embodiment Mode 3 can be referred to for the material and the deposition method of the interlayer insulating layer 150 and the interlayer insulating layer 152.

Note that the interlayer insulating layer 152 is desirably formed so as to have a flat surface.
This is because by forming the interlayer insulating layer 152 so that the surface is flat, an electrode, a wiring, or the like can be preferably formed over the interlayer insulating layer 152 even when the semiconductor device is miniaturized. . Note that the interlayer insulating layer 152 can be planarized by a method such as CMP (chemical mechanical polishing).

Through the above steps, the transistor 162 including the highly purified oxide semiconductor layer 144 is completed (see FIG. 10). In addition, the capacitor 164 is completed.

10 includes an oxide semiconductor layer 144, a source or drain electrode 142a electrically connected to the oxide semiconductor layer 144, a source or drain electrode 142b, an oxide semiconductor layer 144, a source electrode or The gate insulating layer 146 covers the drain electrode 142a, the source or drain electrode 142b, and the gate electrode 148a over the gate insulating layer 146. The capacitor 164 includes a source or drain electrode 142a, an oxide semiconductor layer 144, a gate insulating layer 146 that covers the source or drain electrode 142a, and an electrode 148b over the gate insulating layer 146.

In the transistor 162 described in this embodiment, since the oxide semiconductor layer 144 is highly purified, its hydrogen concentration is 5 × 10 ¹⁹ atoms / cm ³ or less, preferably 5 ×
10 ¹⁸ atoms / cm ³ or less, more desirably 5 × 10 ¹⁷ atoms / cm ³ or less. In addition, the carrier density of the oxide semiconductor layer 144 is sufficiently smaller than the carrier density (about 1 × 10 ¹⁴ / cm ³ ) in a general silicon wafer (for example, 1
× 10 ¹² / cm ³ , more preferably less than 1.45 × 10 ¹⁰ / cm ³ ).
As a result, the off-state current becomes sufficiently small. For example, the off-state current of the transistor 162 at room temperature (here, a value per unit channel width (1 μm)) is 100 zA / μm.
(1zA (zeptoampere) is 1 × 10 ⁻²¹ A) or less, preferably 10 zA / μm or less.

By using the oxide semiconductor layer 144 that is highly purified and intrinsic as described above, the off-state current of the transistor can be sufficiently reduced. By using such a transistor, a semiconductor device that can hold stored data for an extremely long time can be obtained.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

(Embodiment 5)
In this embodiment, a structure and a manufacturing method of a semiconductor device according to one embodiment of the disclosed invention, which are different from those in Embodiments 3 and 4, will be described with reference to FIGS.

<Cross-sectional configuration and planar configuration of semiconductor device>
FIG. 4 illustrates an example of a structure of a semiconductor device. 4A shows a cross section of the semiconductor device in FIG.
B) shows respective planes of the semiconductor device. Here, FIG. 4A shows C in FIG.
It corresponds to a cross section at 1-C2 and D1-D2. In the plan view of FIG. 4B, in order to avoid complication, a source or drain electrode 154, a wiring 156, etc.
Some of the components are omitted. The semiconductor device shown in FIG. 4A and FIG.
The lower portion includes the transistor 160 using a semiconductor material other than an oxide semiconductor, and the upper portion includes the transistor 162 using an oxide semiconductor. The transistor 160 using a semiconductor material other than an oxide semiconductor can operate at high speed by using a material having a field effect mobility higher than that of the oxide semiconductor material. On the other hand, the transistor 162 including an oxide semiconductor material can hold charge for a long time due to its characteristics.

Note that although all the above transistors are described as n-channel transistors, it goes without saying that p-channel transistors can be used. Further, since the technical essence of the disclosed invention is that an oxide semiconductor is used for the transistor 162 in order to retain information, the specific structure of the semiconductor device is not necessarily limited to the one shown here.

One difference between the semiconductor device shown in FIG. 4 and the semiconductor device shown in the above embodiment is a planar layout of the semiconductor device. In this embodiment, the transistor 162 and the capacitor 164 are provided so as to overlap with the transistor 160. By adopting such a planar layout, high integration is possible. For example, the minimum processing dimension is F, and the area occupied by the memory cell can be 15F ^{2 to} 25F ² .

Another difference between the semiconductor device shown in FIG. 4 and the semiconductor device shown in the above embodiment is
The presence or absence of the sidewall insulating layer 118 in the transistor 160. That is, the semiconductor device shown in FIG. 4 does not have a sidewall insulating layer. Further, since the sidewall insulating layer is not formed, the impurity region 114 is not formed. In this manner, when the sidewall insulating layer is not provided, integration is easier than in the case where the sidewall insulating layer 118 is provided. Further, the manufacturing process can be simplified as compared with the case where the sidewall insulating layer 118 is provided.

Another difference between the semiconductor device shown in FIG. 4 and the semiconductor device shown in the above embodiment is
The presence or absence of the interlayer insulating layer 125 in the transistor 160. That is, the semiconductor device illustrated in FIG. 4 includes the interlayer insulating layer 125. By using an insulating layer containing hydrogen as the interlayer insulating layer 125, hydrogen can be supplied to the transistor 160 so that the characteristics of the transistor 160 can be improved. Examples of such an interlayer insulating layer 125 include a silicon nitride layer containing hydrogen formed by a plasma CVD method. Furthermore, the interlayer insulating layer 1
26, by applying an insulating layer in which hydrogen is sufficiently reduced, entry of hydrogen into the transistor 162 that may deteriorate the characteristics of the transistor 162 can be prevented. Examples of such an interlayer insulating layer 126 include a silicon nitride layer formed by sputtering. By adopting such a structure, the characteristics of the transistor 160 and the transistor 162 can be sufficiently improved.

Another difference between the semiconductor device shown in FIG. 4 and the semiconductor device shown in the above embodiment is
The presence or absence of the insulating layer 143a and the insulating layer 143b in the transistor 162. That is, the semiconductor device illustrated in FIG. 4 includes the insulating layer 143a and the insulating layer 143b. In this manner, by providing the insulating layer 143a and the insulating layer 143b, so-called gate capacitance due to the gate electrode 148a and the source or drain electrode 142a (or the gate electrode 148a and the source or drain electrode 142b) is reduced. Transistor 1
The operation speed of 62 can be improved.

Note that as in Embodiment 4, the lower transistor 160 and the upper transistor 162 are
The source or drain electrode 142a is directly formed on the gate electrode 110a to be electrically connected. With such a configuration, the degree of integration is improved as compared with the case where electrodes and wirings are separately provided. Further, the manufacturing process is simplified.

In the present embodiment, a configuration having the above-described differences integrally is shown, but a configuration having only one of the differences may be adopted.

<Method for Manufacturing Semiconductor Device>
Next, an example of a method for manufacturing the semiconductor device will be described. Hereinafter, a process after forming the lower transistor 160 and a method for manufacturing the upper transistor 162 will be described with reference to FIGS. The lower transistor 160 can be manufactured by a method similar to the method described in Embodiment 3. For details, the description of Embodiment Mode 3 can be referred to. Note that in this embodiment, the interlayer insulating layer 125 is formed so as to cover the transistor 160.
Three types of interlayer insulating layers, that is, an interlayer insulating layer 126 and an interlayer insulating layer 128 are formed (
FIG. 8 (G) reference). In this embodiment, in the manufacturing process of the transistor 160,
Although the source or drain electrode 130a and the source or drain electrode 130b are not formed (see FIG. 8H), the source or drain electrode 130a and the source or drain electrode 130b are not formed. For convenience, it will be referred to as a transistor 160.

First, after forming the lower transistor 160 by the method described in Embodiment 3, the upper portion of the upper surface of the gate electrode 110a of the transistor 160 is removed. A polishing process such as CMP (Chemical Mechanical Polishing) may be applied to the removal process. Thereby, the interlayer insulating layer 125, the interlayer insulating layer 126, and the interlayer insulating layer 128 above the upper surface of the gate electrode 110a are removed. Note that, by sufficiently planarizing the surface related to the polishing treatment, favorable electrodes, wirings, insulating layers, semiconductor layers, and the like can be formed in later steps.

Next, a conductive layer is formed over the gate electrode 110a, the interlayer insulating layer 125, the interlayer insulating layer 126, and the interlayer insulating layer 128, and the conductive layer is selectively etched, so that the source or drain electrode 142a, the source electrode or A drain electrode 142b is formed (see FIG. 5A). Here, the source or drain electrode 142a is formed so as to be directly connected to the gate electrode 110a.

The conductive layer for forming the source or drain electrode 142a and the source or drain electrode 142b can be formed using a material similar to that described in Embodiment 3. In addition, the conductive layer can be etched by a method similar to the method described in Embodiment Mode 3. For details, the description of Embodiment Mode 3 can be referred to.

Next, the source or drain electrode 142a, the source or drain electrode 142b
An insulating layer is formed so as to cover the insulating layer, and the insulating layer is selectively etched to form an insulating layer 143a over the source or drain electrode 142a and an insulating layer 143b over the source or drain electrode 142b. (See FIG. 5B).

By providing the insulating layer 143a and the insulating layer 143b, the gate electrode formed later and the source or drain electrode 142a, and the gate electrode formed later and the source or drain electrode 142b are formed. It is possible to reduce the parasitic capacitance.

Next, the source or drain electrode 142a, the source or drain electrode 142b
An oxide semiconductor layer 144 is formed so as to cover the gate insulating layer 1 over the oxide semiconductor layer 144.
46 is formed (see FIG. 5C).

The oxide semiconductor layer 144 can be formed using the materials and methods described in Embodiment 3. The oxide semiconductor layer 144 is preferably subjected to heat treatment (first heat treatment). For details, the description of Embodiment Mode 3 can be referred to.

The gate insulating layer 146 can be formed using the material and method described in Embodiment 3.
In addition, after the gate insulating layer 146 is formed, heat treatment (second heat treatment) is preferably performed in an inert gas atmosphere or an oxygen atmosphere. For details, the description of Embodiment Mode 3 can be referred to.

Next, over the gate insulating layer 146, a gate electrode 148a is formed in a region overlapping with a region to be a channel formation region of the transistor 162, and the source or drain electrode 142 is formed.
An electrode 148b is formed in a region overlapping with a (see FIG. 5D).

The gate electrode 148a and the electrode 148b can be formed by forming a conductive layer over the gate insulating layer 146 and then selectively etching the conductive layer. The conductive layer to be the gate electrode 148a and the electrode 148b is formed by a PVD method such as a sputtering method,
It can be formed using a CVD method such as a plasma CVD method. The details are the same as those of the source electrode or the drain electrode 142a, and the description thereof can be referred to.

Next, the interlayer insulating layer 150 and the interlayer insulating layer 152 are formed over the gate insulating layer 146, the gate electrode 148a, and the electrode 148b (see FIG. 6A). The interlayer insulating layer 150 and the interlayer insulating layer 152 can be formed using the materials and methods described in Embodiment 3. For details, the description of Embodiment Mode 3 can be referred to.

Note that the interlayer insulating layer 152 is desirably formed so as to have a flat surface.
This is because by forming the interlayer insulating layer 152 so that the surface is flat, an electrode, a wiring, or the like can be preferably formed over the interlayer insulating layer 152 even when the semiconductor device is miniaturized. . Note that the interlayer insulating layer 152 can be planarized by a method such as CMP (chemical mechanical polishing).

Next, the interlayer insulating layer 125, the interlayer insulating layer 126, the interlayer insulating layer 128, and the oxide semiconductor layer 144
The gate insulating layer 146, the interlayer insulating layer 150, and the interlayer insulating layer 152 are selectively etched, so that an opening reaching the metal compound region 124 of the transistor 160 is formed (FIG. 6B).
reference). As etching, either dry etching or wet etching may be used. From the viewpoint of miniaturization, it is desirable to use dry etching.

Then, a source or drain electrode 154 is formed so as to be embedded in the opening.
Then, a wiring 156 connected to the source or drain electrode 154 is formed (FIG. 6 (
C)).

For the source or drain electrode 154, for example, after a conductive layer is formed in a region including an opening using a PVD method, a CVD method, or the like, a part of the conductive layer is removed using a method such as etching or CMP. Can be formed. More specifically, for example, a method in which a titanium film is thinly formed by a PVD method in a region including an opening, a titanium nitride film is thinly formed by a CVD method, and then a tungsten film is formed so as to be embedded in the opening is applied. Can do. Here, the titanium film formed by the PVD method has a function of reducing an oxide film (natural oxide film or the like) on the surface to be formed and reducing contact resistance with the lower electrode or the like (here, the metal compound region 124). . The titanium nitride film formed thereafter has a barrier function that suppresses diffusion of the conductive material. Further, after forming a barrier film made of titanium, titanium nitride, or the like, a copper film may be formed by a plating method.

The wiring 156 can be formed by forming a conductive layer in contact with the source or drain electrode 154 and then selectively etching the conductive layer. The conductive layer is
The film can be formed by a PVD method such as a sputtering method or a CVD method such as a plasma CVD method. The details are the same as in the case of the source or drain electrode 142a.

Through the above steps, a semiconductor device including the transistor 160, the transistor 162, and the capacitor 164 is completed.

In the semiconductor device described in this embodiment, the transistor 162 and the capacitor 164 are provided so as to overlap with the transistor 160, the transistor 160 does not have a sidewall insulating layer, the source electrode or the gate electrode 110a High integration is possible because the drain electrode 142a is formed directly. In addition, the manufacturing process is simplified.

In the semiconductor device described in this embodiment, an insulating layer containing hydrogen is used as the interlayer insulating layer 125, and an insulating layer in which hydrogen is sufficiently reduced is used as the interlayer insulating layer 126, whereby the transistor 160 The characteristics of the transistor 162 are improved. Insulating layer 14
By having 3a and the insulating layer 143b, so-called gate capacitance is reduced and the operation speed of the transistor 162 is improved.

With the above-described characteristics described in this embodiment, a semiconductor device with extremely excellent characteristics can be provided.

The structures, methods, and the like described in this embodiment can be combined as appropriate with any of the structures, methods, and the like described in the other embodiments.

(Embodiment 6)
In this embodiment, the case where the semiconductor device described in any of the above embodiments is applied to an electronic device will be described with reference to FIGS. In this embodiment, a computer, a mobile phone (also referred to as a mobile phone or a mobile phone device), a mobile information terminal (including a portable game machine, an audio playback device, etc.), a digital camera, a digital video camera, electronic paper, a television The case where the above-described semiconductor device is applied to an electronic device such as a device (also referred to as a television or a television receiver) will be described.

FIG. 12A illustrates a laptop personal computer, which includes a housing 701, a housing 702,
A display unit 703, a keyboard 704, and the like are included. A housing 701 and a housing 702
Inside, the semiconductor device described in any of the above embodiments is provided. Therefore, a laptop personal computer is realized in which information is written and read at high speed, memory can be retained for a long time, and power consumption is sufficiently reduced.

FIG. 12B illustrates a personal digital assistant (PDA). A main body 711 is provided with a display portion 713, an external interface 715, operation buttons 714, and the like. A stylus 712 for operating the portable information terminal is also provided. In the main body 711, the semiconductor device described in any of the above embodiments is provided. Therefore, writing and reading of information is fast,
A portable information terminal that can retain data for a long period of time and has sufficiently reduced power consumption is realized.

FIG. 12C illustrates an e-book reader 720 mounted with electronic paper, which includes a housing 721 and a housing 72.
3 of two housings. Each of the housing 721 and the housing 723 includes a display portion 7.
25 and a display portion 727 are provided. The housing 721 and the housing 723 are connected by a shaft portion 737 and can be opened and closed with the shaft portion 737 as an axis. The housing 7
21 includes a power source 731, an operation key 733, a speaker 735, and the like. Housing 721
At least one of the housings 723 is provided with the semiconductor device described in the above embodiment.
Therefore, an electronic book can be realized in which information is written and read at high speed, memory can be stored for a long time, and power consumption is sufficiently reduced.

FIG. 12D illustrates a mobile phone, which includes two housings, a housing 740 and a housing 741. Further, the housing 740 and the housing 741 can be slid to be in an overlapped state from the deployed state as illustrated in FIG. 12D, and can be reduced in size to be portable. The housing 741 includes a display panel 742, a speaker 743, a microphone 744, a pointing device 746, a camera lens 747, an external connection terminal 748, and the like. The housing 740 includes a solar battery cell 749 for charging the mobile phone, an external memory slot 750, and the like. The antenna is incorporated in the housing 741. Case 7
At least one of 40 and the housing 741 is provided with the semiconductor device described in the above embodiment. Therefore, a mobile phone in which information is written and read at high speed, memory can be stored for a long time, and power consumption is sufficiently reduced is realized.

FIG. 12E illustrates a digital camera, which includes a main body 761, a display portion 767, an eyepiece portion 763, operation switches 764, a display portion 765, a battery 766, and the like. In the main body 761, the semiconductor device described in any of the above embodiments is provided. Therefore, a digital camera can be realized in which writing and reading of information are performed at high speed, storage for a long period of time is possible, and power consumption is sufficiently reduced.

FIG. 12F illustrates a television device 770 which includes a housing 771, a display portion 773, a stand 775, and the like. The television device 770 can be operated with a switch included in the housing 771 or a remote controller 780. The semiconductor device described in any of the above embodiments is mounted on the housing 771 and the remote controller 780. Therefore, a television device which can write and read information at high speed, can store data for a long time, and has sufficiently reduced power consumption is realized.

As described above, the electronic device described in this embodiment includes the semiconductor device according to any of the above embodiments. For this reason, an electronic device with reduced power consumption is realized.

The number of rewritable times of the semiconductor device according to one embodiment of the disclosed invention was investigated. In this embodiment, the investigation result will be described with reference to FIG.

The semiconductor device used for the investigation is a semiconductor device having a circuit configuration illustrated in FIG. Here, an oxide semiconductor is used for a transistor corresponding to the transistor 162, and the capacitor 164 is used.
As a capacitive element corresponding to, a capacitor having a capacitance value of 0.33 pF was used.

The investigation was performed by comparing the initial memory window width with the memory window width after repeating the holding and writing of information a predetermined number of times. In order to retain information and write information, 0 V or 5 V is applied to the wiring corresponding to the third wiring in FIG. 1A-1 and 0 V or 5 V is applied to the wiring corresponding to the fourth wiring. Done by giving one of them. When the potential of the wiring corresponding to the fourth wiring is 0 V, the transistor 162
Since the transistor corresponding to (the writing transistor) is off, the node FG
The potential applied to is held. When the potential of the wiring corresponding to the fourth wiring is 5 V, the transistor corresponding to the transistor 162 is on, so that the potential of the wiring corresponding to the third wiring is supplied to the node FG.

The memory window width is one index indicating the characteristics of the storage device. Here, a curve (V) showing the relationship between the potential Vcg of the wiring corresponding to the fifth wiring and the drain current Id of the transistor (reading transistor) corresponding to the transistor 160 between different memory states.
(cg-Id curve) of the shift amount ΔVcg. The different storage states refer to a state in which 0V is applied to the node FG (hereinafter referred to as a Low state) and a state in which 5V is applied to the node FG (hereinafter referred to as a High state). In other words, the memory window width is Low
This can be confirmed by sweeping the potential Vcg in the high state and the high state.

FIG. 13 shows the results of examining the memory window width in the initial state and the memory window width after writing 1 × 10 ⁹ times. In FIG. 13, the horizontal axis represents Vcg (V), and the vertical axis represents Id (A). From FIG. 13, it can be confirmed that the memory window width does not change before and after the writing of 1 × 10 ⁹ times. The fact that the memory window width does not change before and after 1 × 10 ⁹ writes indicates that the semiconductor device does not deteriorate at least during this period.

As described above, the semiconductor device according to one embodiment of the disclosed invention, hold and write ¹⁰⁹
Even if repeated many times, the characteristics do not change and the rewriting resistance is extremely high. That is, according to one embodiment of the disclosed invention, a highly reliable semiconductor device can be realized.

In this example, the result of obtaining the off-state current of a transistor including a highly purified oxide semiconductor will be described.

In this example, according to Embodiment 3, a transistor was manufactured using a highly purified oxide semiconductor. First, in consideration of a sufficiently small off-state current of a transistor including a highly purified oxide semiconductor, a transistor having a sufficiently large channel width W of 1 m was prepared, and off-state current was measured. FIG. 14 shows the result of measuring the off-state current of a transistor having a channel width W of 1 m. In FIG. 14, the horizontal axis represents the gate voltage VG, and the vertical axis represents the drain current ID. When the drain voltage VD is + 1V or + 10V, the gate voltage VG is changed from -5V to -2
In the range of 0 V, the off-state current of the transistor was found to be 1 × 10 ⁻¹³ A or less, which is the detection limit. Further, the off-state current of the transistor (here, the unit channel width (1 μm
)) Was 1 aA / μm (1 × 10 ⁻¹⁸ A / μm) or less.

Next, a result obtained by more accurately obtaining the off-state current of a transistor including a highly purified oxide semiconductor will be described. As described above, it was found that the off-state current of a transistor including a highly purified oxide semiconductor is 1 × 10 ⁻¹³ A or less, which is the detection limit of the measuring instrument. Therefore, a description will be given of a result obtained by fabricating a characteristic evaluation element and obtaining a more accurate off-current value (a value equal to or lower than the detection limit of the measuring device in the above measurement).

First, the element for characteristic evaluation used in the current measurement method will be described with reference to FIG.

In the element for characteristic evaluation shown in FIG. 15, three measurement systems 800 are connected in parallel. Measurement system 80
0 represents a capacitor 802, a transistor 804, a transistor 805, and a transistor 806
, A transistor 808 is included. As the transistors 804, 805, and 806, transistors manufactured according to Embodiment 3 were used.

In the measurement system 800, one of the source terminal and the drain terminal of the transistor 804,
One terminal of the capacitor 802 and one of the source terminal and the drain terminal of the transistor 805 are connected to a power source (a power source that supplies V2). The other of the source terminal and the drain terminal of the transistor 804, one of the source terminal and the drain terminal of the transistor 808, the other terminal of the capacitor 802, and the gate terminal of the transistor 805 are connected. The other of the source terminal and the drain terminal of the transistor 808, one of the source terminal and the drain terminal of the transistor 806, and the gate terminal of the transistor 806 are connected to a power source (a power source that supplies V1). In addition, the other of the source terminal and the drain terminal of the transistor 805 and the other of the source terminal and the drain terminal of the transistor 806 are connected to serve as an output terminal Vout.

Note that the gate terminal of the transistor 804 is supplied with a potential Vext_b2 for controlling the on state and the off state of the transistor 804, and the potential Vext_b1 for controlling the on state and the off state of the transistor 808 is supplied to the gate terminal of the transistor 808. Is supplied.
Further, the potential Vout is output from the output terminal.

Next, a current measurement method using the above measurement system will be described.

First, an outline of an initialization period in which a potential difference is applied in order to measure off current will be described.
In the initialization period, a potential Vext_b1 that turns on the transistor 808 is input to the gate terminal of the transistor 808, and a node connected to the other of the source terminal and the drain terminal of the transistor 804 (that is, the source terminal of the transistor 808) A potential V1 is applied to a node A which is one of the drain terminal, the other terminal of the capacitor 802, and a node connected to the gate terminal of the transistor 805. Here, the potential V1 is, for example, a high potential. The transistor 804 is kept off.

After that, the potential Vext_b1 that turns off the transistor 808 is input to the gate terminal of the transistor 808, so that the transistor 808 is turned off. Transistor 808
Is turned off, the potential V1 is set to a low potential. Again, the transistor 804 is kept off. The potential V2 is the same as the potential V1. Thus, the initialization period ends. In the state where the initialization period is completed, a potential difference is generated between the node A and one of the source electrode and the drain electrode of the transistor 804, and the node A and the transistor 808
Since a potential difference is generated between the other of the source electrode and the drain electrode, a slight amount of charge flows through the transistor 804 and the transistor 808. That is, an off current is generated.

Next, an outline of the off-current measurement period will be described. In the measurement period, the potential of one of the source terminal and the drain terminal of the transistor 804 (that is, V2) and the potential of the other terminal of the source and drain terminals of the transistor 808 (that is, V1) are fixed to a low potential. Keep it. On the other hand, during the measurement period, the potential of the node A is not fixed (set to a floating state). Thus, charge flows through the transistor 804, and the amount of charge held at the node A varies with time. Then, the potential of the node A varies as the amount of charge held in the node A varies. That is, the output potential Vout of the output terminal also varies.

FIG. 16 shows details (timing chart) of the relationship between each potential in the initialization period in which the potential difference is applied and in the subsequent measurement period.

In the initialization period, first, the potential Vext_b2 is set to a potential (a high potential) at which the transistor 804 is turned on. As a result, the potential of the node A is V2, that is, a low potential (
VSS). After that, the potential Vext_b2 is set to a potential (low potential) at which the transistor 804 is turned off, so that the transistor 804 is turned off. Then, the potential Vext_b1 is set to a potential (high potential) at which the transistor 808 is turned on. As a result, the potential of the node A becomes V1, that is, the high potential (VDD). After that, the potential Vext_b1 is set to a potential at which the transistor 808 is turned off. As a result, the node A enters a floating state, and the initialization period ends.

In the subsequent measurement period, charges flow into the node A from the potential V1 and the potential V2,
Alternatively, the potential is such that charge flows from the node A. Here, the potential V1 and the potential V
2 is a low potential (VSS). However, since it is necessary to operate the output circuit at the timing of measuring the output potential Vout, V1 may be temporarily set to the high potential (VDD). Note that the period during which V1 is set to the high potential (VDD) is set to a short period that does not affect the measurement.

When the potential difference is applied as described above and the measurement period is started, the amount of charge held in the node A varies with time, and the potential of the node A varies accordingly. This means that the potential of the gate terminal of the transistor 805 fluctuates. Therefore, the potential of the output potential Vout of the output terminal also changes with the passage of time.

A method for calculating the off current from the obtained output potential Vout will be described below.

Prior to calculation of the off-state current, a relationship between the potential VA of the node A and the output potential Vout is obtained. Thereby, the potential VA of the node A can be obtained from the output potential Vout. From the above relationship, the potential VA of the node A can be expressed as the following equation as a function of the output potential Vout.

Further, the charge QA of the node A is expressed by the following equation using the potential VA of the node A, the capacitance CA connected to the node A, and a constant (const). Here, the capacitor CA connected to the node A is the sum of the capacitor of the capacitor 802 and other capacitors.

Since the current IA at the node A is a time derivative of the charge flowing into the node A (or the charge flowing out from the node A), the current IA at the node A is expressed by the following equation.

As described above, the current IA of the node A can be obtained from the capacitor CA connected to the node A and the output potential Vout of the output terminal.

By the method described above, leakage current (off-state current) flowing between the source and drain of the transistor in the off state can be measured.

In this example, the transistor 804, the transistor 805, the transistor 806, and the transistor 808 were manufactured using a highly purified oxide semiconductor having a channel length L = 10 μm and a channel width W = 50 μm. Further, in each of the measurement systems 800 arranged in parallel, the capacitive element 802
The capacitance values of a, 802b, and 802c were 100 fF for the capacitive element 802a, 1 pF for the capacitive element 802b, and 3 pF for the capacitive element 802c, respectively.

In the measurement according to this example, VDD = 5V and VSS = 0V. In the measurement period, the potential V1 is set to VSS in principle, and every 10 to 300 sec, 100 mse.
Vout was measured as VDD only during period c. Further, Δt used for calculation of the current I flowing through the element was about 30000 sec.

FIG. 17 shows the relationship between the elapsed time Time for the current measurement and the output potential Vout.
From FIG. 17, it can be confirmed that the potential changes as time passes.

FIG. 18 shows the off current calculated by the current measurement. FIG. 18 shows the relationship between the source-drain voltage V and the off-current I. FIG. 18 shows that the off-state current is about 40 zA / μm at room temperature under the condition where the source-drain voltage is 4V. Further, the off-state current is 10 zA at room temperature under the condition that the source-drain voltage is 3.1 V.
/ Μm or less. Incidentally, 1 zA represents ^{10 -21} A.

As described above, according to this example, it was confirmed that the off-state current of the transistor including a highly purified oxide semiconductor is sufficiently small.

DESCRIPTION OF SYMBOLS 100 Substrate 102 Protective layer 104 Semiconductor region 106 Element isolation insulating layer 108a Gate insulating layer 110a Gate electrode 112 Insulating layer 114 Impurity region 116 Channel formation region 118 Side wall insulating layer 120 High concentration impurity region 122 Metal layer 124 Metal compound region 125 Interlayer insulation Layer 126 interlayer insulating layer 128 interlayer insulating layer 130a source or drain electrode 130b source or drain electrode 130c electrode 142a source or drain electrode 142b source or drain electrode 143a insulating layer 143b insulating layer 144 oxide semiconductor layer 146 gate insulating layer 148a Gate electrode 148b Electrode 150 Interlayer insulating layer 152 Interlayer insulating layer 154 Source or drain electrode 160 Transistor 162 Transistor 164 Capacitance element 7 DESCRIPTION OF SYMBOLS 1 Case 702 Case 703 Display part 704 Keyboard 711 Main body 712 Stylus 713 Display part 714 Operation button 715 External interface 720 Electronic book 721 Case 723 Case 725 Display part 727 Display part 731 Power supply 733 Operation key 735 Speaker 737 Shaft part 740 Housing 741 Housing 742 Display panel 743 Speaker 744 Microphone 746 Pointing device 747 Camera lens 748 External connection terminal 749 Solar cell 750 External memory slot 761 Main body 763 Eyepiece 764 Operation switch 765 Display 766 Battery 767 Display 770 Television John Device 771 Case 773 Display 775 Stand 780 Remote control device 802 Capacitance element 802a Capacitance element 802b Capacitance element 802c Capacitance element 80 Transistor 805 transistor 806 transistor 808 transistor

Claims (1)

A first transistor having a first channel formation region;
A first insulating layer located above the first channel formation region and having a contact hole;
A first conductive layer located in the contact hole;
A second transistor located above the first insulating layer and having a second channel formation region;
A second conductive layer above the first insulating layer;
A capacitive element above the first insulating layer,
The first conductive layer and the second conductive layer are electrically connected,
The first conductive layer has a region functioning as one of a source electrode and a drain electrode of the first transistor,
The second conductive layer is formed through a step of processing the same conductive layer as one of the source electrode or the drain electrode of the second transistor,
A gate electrode of the first transistor, one of a source electrode or a drain electrode of the second transistor, and one electrode of the capacitor are electrically connected;
The first insulating layer has a first layer and a second layer above the first layer;
The semiconductor device, wherein the first layer contains hydrogen at a higher concentration than the second layer.